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← ↑ → The appliance technician must be familiar with the procedures used to install and service room air-conditioning units. The installation of these types of units is varied, de pending on the make, model, and the type of structure in which the unit is to be installed. However, the servicing of room units is not as varied. Standard service procedures can be used on almost any unit with great success. Because of this we won’t include the installation procedures in this book. It’s recommended that the service technician refer to the installation instructions packaged with the unit being installed. CONSTRUCTION AND OPERATION The following is a description of the construction and operation of room air-conditioning units. Construction Referring to Fgr. 1, the refrigeration components of a typical room air-conditioning unit are mounted on a heavy steel base pan that is protected from the elements by a durable enamel finish. The evaporator and condenser are positioned so that they can be served by a single-fan motor. The evaporator sits on an insulated condensate drain tray. The compressor is mounted to the base pan by welded studs that pass through the compressor base brackets. Rubber grommets are used to cushion the compressor and re duce sound transmission. Retaining nuts and washers se cure the compressor to the studs. An insulated bulkhead separates the room-side components (evaporator, evaporator blower, and electrical controls) from the outside components (compressor, con denser, condenser fan, and fan motor). An enamel-finished cabinet shell houses the entire assembly, protecting the components. The cabinet leaves the back side of the condenser exposed. It’s louvered either on both sides or in the rear to provide inlet air for the condenser fan. Some models have a removable rear grille that protects the condenser without restricting the air flow over the condenser. The front of the cabinet is open, with the edges formed to accept the decorative front panel. The cabinet of larger units is partially enclosed on the bottom, providing support for the air- conditioning unit. The unit can be pulled out of the cabinet for service. Fgr. 1 Refrigeration components of a room air-conditioning unit. Air flow through the evaporator and the condenser is provided by a double-shaft fan motor mounted to the back side of the center partition. The condenser fan operates within a shroud enclosing the front side of the condenser. The condenser fan blows outside air through the condenser fins. On almost all models, the room air is drawn through the evaporator by a squirrel cage blower wheel or a propeller-type fan. The air is then discharged into a full-width plenum located directly above the evaporator. Occasionally, the evaporator will be located in front of the plenum. In this design, the air is blown through the evaporator. In either case, the unit is designed to provide cooling at the rate specified on the nameplate. All the exterior surfaces of the blower or fan housing and the plenum that are exposed to the outside air are insulated to prevent any loss of cooling capacity. The surfaces of the cabinet that are exposed to refrigerated air are insulated to prevent sweating (condensation). The electric controls are mounted to a metal plate that is attached to a metal box located adjacent to the evaporator, thus providing a safety enclosure for the controls. An escutcheon, with operating instructions and control knobs, completes the control assembly. There are several different cabinet designs to accommodate the various size, capacity, and installation conditions. Models are available with an electric heater coil mounted in the discharge plenum. The installation kits are varied for the different installations that may be encountered. Operation: The room air conditioner is designed to circulate, ventilate, filter, cool, dehumidify, and, with some models, heat rooms in homes, offices, and other closed areas where a comfortable ambient is desired. Most models can be operated through the use of two- or three-speed fans to provide the amount and degree of air conditioning needed for maxi mum comfort. Adjustable louvers allow the user to direct the conditioned air to maximize the unit’s effectiveness. To rid the air of unwanted odors or to maintain a freshness in the air, some models are equipped with an exhaust door installed in the discharge air plenum. When opened, a small percent age of the recirculated air is discharged to the outside. Fresh air infiltrates the building structure to replace the exhausted air. Some louver designs provide the ability to close off a portion or all of the cold-air outlet, thereby increasing the exhaust. Filtering is accomplished through the use of a clean able, plastic foam filter sheet that is placed in the return air stream. This filter is either attached directly to the face of the evaporator by pressing it onto bayonet-type retainers (solid-front models), or it’s held against the back side of the Condenser--Evaporator air intake grille of the decorative cabinet front by plastic tabs (grille-front models). Pull-and-clean filters come with products that have a tip-out front grille. Cooling is provided by operating the compressor along with the fan. On most models, room air is drawn through the front panel, the filter, and evaporator by the evaporator fan, and discharged into the plenum and back into the room. As the air passes over the evaporator fins, it’s cooled. Excessive moisture is also condensed from it. The condensate runs off the evaporator into a plastic drain tray under the evaporator. It then flows through a tube past the cabinet bulkhead and into a trough stamped into the base pan. This water is collected in a sump under the condenser fan. The condensate water is picked up by the fan and thrown onto the condenser where it evaporates, significantly increasing the efficiency and capacity of the unit. A variable rate of cooling is provided by operating the unit at the various fan speeds available. The operation of the air conditioner is controlled by a thermostat that senses the temperature of the room air as it enters the unit. When the room air temperature drops to the cutoff setting of the thermostat, it turns off the compressor. The fan motor remains running to keep the room air circulating over the thermostat. This causes the air conditioner to respond quickly to changes in the overall room temperature. Some models feature an energy-saving switch that causes the fan to cycle off and on with the compressor. Most people find the constant air movement more comfortable. FUNCTIONAL SYSTEMS: The following is a discussion of the functional systems of a room air-conditioning unit. Sealed Refrigeration System Referring to Fgr. 2, a typical sealed refrigeration system consists of a cooling coil (evaporator) located on the room side, a heat rejection coil (condenser) located outside, and an electric self-contained, motor/compressor to circulate a refrigerant through the system and to develop the necessary pressure differential to make the system work. Copper tubing, sized to carry the volume of refrigerant to be circulated, connects these components in a continuous loop—from the evaporator to the compressor to the con denser and back to the evaporator. The tube connecting the condenser to the evaporator also serves as a refrigerant flow control. This tube (restrictor tube) has a very small inside diameter. The combination of this small diameter and the extra length of this tube restricts the flow of liquid refrigerant, maintaining the pressure differential necessary for the refrigeration system to function as designed. A cone-shaped strainer is placed in the condenser outlet tube to prevent any foreign material from clogging the restrictor tube. On some large units, an automatic (expansion) valve, located at the evaporator inlet, is used for refrigerant flow control. Operation of the sealed refrigeration system---Operation of the refrigeration system involves three basic physical laws: 1. The physical state of a substance (solid, liquid, or gas) is directly related to the heat contained in the substance. 2. A large amount of heat is required to change the state of a substance (solid to liquid, liquid to gas, and vice versa) with no change in its temperature. 3. The temperature at which a substance changes from a liquid to a gas and a gas to a liquid depends on the pressure on the substance. Fgr. 3 illustrates a typical refrigeration system, indicating the pressure, temperature, and physical state of the refrigerant throughout the system during the refrigeration cycle as described below. Fgr. 2 Typical sealed refrigeration system. Fgr. 3 Operation of a typical refrigeration system. Compressor Low pressure saturated gas plus absorbed heat Cooler drier air Inside; Warm moist _______ Low pressure liquid minus absorbed heat Evaporator---Condenser; High pressure liquid minus absorbed heat; Warm humid air In operation, the compressor lowers the pressure on the liquid refrigerant in the evaporator to the point at which the refrigerant will change from a liquid to a gas at temperatures ranging between 35 and 50°F. The heat required for this change is obtained from the room air circulated through the evaporator fins. Heat is absorbed by the refrigerant not only from the air, but from the moisture in the air as well. The air is cooled and the moisture condenses on the evaporator fins. As the refrigerant liquid continues to vaporize, the pressure in the evaporator tends to rise. However, the compressor removes the vapor at a rate which maintains the desired pressure and temperature in the evaporator. The compressor discharges the refrigerant gas into the condenser where the pressure builds up against the restrictor tube. As the pressure of the gas increases, so does its temperature. When the temperature of the gas in the condenser exceeds the temperature of the air passing through the condenser, heat is transferred from the gas to the outside air. This loss of heat causes the refrigerant gas to condense back to a liquid. The small-diameter restrictor tube between the con denser and the evaporator maintains the pressure differential created by the compressor. It also meters the liquid refrigerant back into the evaporator. The refrigeration cycle is now complete and will continue until the compressor is turned off by the thermostat. Air-Handling Systems: The following is a discussion of the air handling systems used on room air-conditioning units. Room air circulation---A blower wheel, or propeller fan, pulls the warm humid air through the air filter and evaporator where it’s cleaned, cooled, and dehumidified. The conditioned air is then discharged through the plenum and a louvered grille into the room. Most models have both horizontal and vertical louvers. The downward movement of the horizontal louvers is restricted to prevent recirculating the cold air directly over the thermo stat. To do so would cause short cycling of the unit. The vertical louvers, on some models, can be closed completely on one or both sides of the air discharge grille to increase the velocity of the discharge air or to maximize the exhaust feature for clearing smoke and/or odors from the room. Most models of room air conditioners have a small exhaust door located in the discharge air plenum. This door is cable operated from the control panel. The amount of air circulated can be varied by selecting from the fan speeds available (up to three speeds on some models). It should be noted that the position of the blower wheel or fan with the blower wheel or fan scroll is critical as to the amount of air delivered into the room. On blow-through models, the warm humid air is pulled through the filter and discharged through the evaporator where it’s cooled and dehumidified before reentering the room. Condenser air---A propeller fan pulls outside air through the cabinet-side louvers and discharges that air through the condenser, carrying away the heat removed from the room by the refrigeration system. A slinger ring (molded onto the outside of the fan blades) or a vortex chamber (molded into the bottom part of the condenser fan shroud) enables the fan to pick up condensate water that has drained away from the evaporator and to throw it onto the condenser. This helps to cool the con denser significantly. Driven by the same motor, the con denser fan speed varies with the evaporator fan speed. On some models with solid side cabinets, the condenser does not extend completely across the cabinet. An open area adjacent to the condenser is provided through which fresh air is drawn. The air is then blown through the condenser. Fgr. 4 Air circulation through the evaporator. Air filter— Horizontal louvers restrict downward movement of cool air. Cooler drier; Decorative front; Evaporator; Condensate tray; Condenser shroud, Outside air plus rejected heat Fgr. 5 Location of the slinger ring. Fresh air intake Fgr. 6 Fresh air intake. The fins on the half of the condenser nearest to the fresh air intake are slanted away from the air intake. This directs the warm air coming from the condenser away from the intake. See Fgr. 6. It should be noted that the position of the fan within the fan shroud is critical as to the amount of air delivered through the condenser. Condensate Water Disposal System The following is a description of the condensate water disposal system components and their operation: 1. Slinger ring design: The slinger ring is attached to the outer circumference of the condenser fan. It picks up condensate water that has drained from the cooling coil and throws it onto the condenser. This disposes of the condensate water and increases the efficiency of the unit through the evaporative cooling effect on the condenser 2. Vortex chamber design A vortex chamber is molded into the bottom of part of the condenser fan shroud. Condensate water from the evaporator flows into a sump below the chamber. The condenser fan blades create a vacuum inside the chamber forming a vortex which pulls water up from the base pan and onto the fan blades. A small amount of water is put into the air stream and onto the condenser fins, while the remainder is recycled. Slinger ring on fan blade picks up condensate water from evaporator and throws it onto condenser coil. Slinger ring Fgr. 8 Location and operation of the vortex chamber. Fgr. 7 Operation of the slinger ring. Note: On through-the-wall heat/cool models, a thermostatic .±rain valve empties the base pan of all water when the outside temperature drops below 40°F. See Fgr. 9. This prevents the fan motor from stalling should the condensate water freeze around the blades during winter operation. FUNCTIONAL COMPONENTS Functional components are those that cause the system to operate as designed. Refrigeration Components These are the components that allow the refrigerant to either circulate or cause it to be circulated to cool and dehumidify the room air as it passes through the unit. Compressor/compressor motor A direct-drive motor compressor assembly is spring-mounted within a welded steel shell. The motor is a permanent split capacitor PSC) type with either an external or an internal motor overload protector. (See the Electrical Controls section presented later in this section.) The electrical connections to the compressor motor are attached to a glass-insulated terminal assembly that is fused into an opening in the steel shell. The compressor is equipped with suction and discharge mufflers o reduce the sound level. The entire assembly is bolted to the air-conditioner base where it’s cushioned by rubber grommets. — Drain valve Fgr. 9 Location and operation of the drain valve. There are two types of compressors used in modern room air conditioners. Some models are equipped with low- side reciprocating piston-type compressors. Other models are equipped with high-side rotary compressors. An important difference to remember when servicing these two types of compressors is the operating refrigerant pressures in the compressor shell. Reciprocating compressors operate with the low side of the suction pressure within the compressor shell. See Fgr. 10. Refrigerant vapor from the evaporator is drawn into the shell to cool the motor windings before being compressed. The high-pressure vapor is discharged directly into the condenser. Vortex chamber
Fgr. 10 Reciprocating compressor. In a rotary compressor, the low-pressure refrigerant vapor from the evaporator is drawn directly into the compression chamber. The high-pressure vapor is discharged into the compressor shell where it picks up excessive motor heat before passing into the condenser. After an extended down time, rotary compressors take longer to start the refrigeration process than reciprocating compressors. The reason is that while the temperature of the evaporator and condenser changes with the fluctuation of ambient temperature, neither type of compressor can provide a temperature-stable mass. Since all of the refrigerant in the system condenses in the compressor shell during extended idle periods, the high-side rotary compressor depends on the heat generated by the motor and compressor to vaporize the refrigerant and pump it through the system. On the other hand, the low-side reciprocating compressor quickly lowers the pressure on the liquid, causing it to vaporize faster. The compressor immediately starts to pump it through the system. The motors of both the reciprocating and the rotary compressors are PSC (permanent split capacitor) motors with both starting and running windings. The starting de vice is the running capacitor connected between the starting winding S terminal and the running winding R terminal. (See the Electrical Diagrams presented at the end of this section.) The capacitance (in microfarads) and voltage of the running capacitor must be rated as indicated by the manufacturer. The run capacitor must be sized according to the manufacturer’s specifications, unless a starting problem is encountered. In such cases see the Start Assist Device section presented later in this section. Too high a capacitance rating will cause overheating of the compressor motor. It may also cause damage to the start windings because of the excessive winding current and temperature. The motor starting torque, while not as high as with a relay and a starting capacitor combination, is more than adequate for air-conditioner operation. Also, the maintenance of a relay and starting capacitor is eliminated. Fgr. 11 Rotary compressor These permanent split capacitor (PSC) compressors must have the rated voltage applied for starting. The applied voltage must be within ±5 percent of the rated voltage at the moment the compressor is attempting to start. To test the compressor, use the following procedure: The compressor can be tested by conducting a capacity test. Don’t attempt to pull a vacuum to test the compressor valves. The compressor motor could be damaged. To test the compressor motor, use the following procedure: Caution: Use extreme care in removing and replacing electrical connections to the compressor terminals. Damage to the terminal assembly can result in an expulsion of a terminal, hot refrigerant, and oil under pressure. Note: Since the compressor is driven by a permanent split capacitor motor, the running capacitor should be tested first. Refer to the capacitor test procedure in the Electrical Controls section presented later in this section. 1. Disconnect the air conditioner from the electrical power. 2. Remove the electrical leads from the compressor terminals. 3. Check the compressor for grounded windings by checking from each terminal to any copper tubing connected directly to the compressor. If continuity is indicated, the motor windings are grounded and the compressor will have to be replaced. 4. Check for open windings by checking from the start terminal to the run terminal. If no continuity is indicated, one of the windings is open and the compressor will have to be replaced. Circuit breaker or fuse rated for compressor full load amps To COMMON (C) terminal on compressor To compressor shell To RUN (R) terminal on compressor To START (5) terminal on compressor Fgr. 12 Compressor test cord. 5. For compressors with an internal overload protector: If continuity is indicated in step 4, then check from COMMON to START and COMMON to RUN. Check the resistance of the start and running windings with the information concerning the specific compressor being tested. If no continuity is indicated, the internal motor protector is open, and the compressor must be given lime for the wind tugs to cool below 172°F and then be rechecked. This may take quite some time. After the compressor has cooled and the continuity from COMMON to START and COMMON to RUN is re stored, the cause of the overloading and overheating of the compressor must be determined. Some possible causes are: 1. Shorted winding Recheck the resistance of the start and run windings and compare this with the information for the compressor being tested. 2. Low voltage Check the voltage at the electrical out let with the air conditioner disconnected, and again at the compressor (COMMON TO RUN) when the compressor starts and while it’s running. Excessive voltage drop during start-up or while it’s running may be the cause of the motor protector opening. 3. Defective run capacitor If the compressor won’t start (or starts slowly) or the compressor runs but draws high current, then test the capacitor. 4. Short cycling on the thermostat Note: This problem has been eliminated on models with electronic controls. The compressors are automatically prevented from restarting for 3 to 4 minutes after a shutoff by an electronic timing switch and relay. 5. Dirty condenser. 6. Insufficient aft flow over the condenser from other causes. If an internal motor protector does not reset after the motor windings have cooled below 172°F, a defective protector is indicated. The compressor will have to be replaced. The compressor can also be operated on a test cord when connected as illustrated in Fgr. 12. Caution: Use only a known good electrolytic capacitor rated for the compressor being tested. The capacitor is a running capacitor. It must be in the circuit while the compressor s running. Evaporator The evaporators used on all air-conditioner models are of the tube-and-fin type. The aluminum fins are punched to fit over staggered rows of copper tubing. The evaporators used on energy-efficient units have refinements to improve the rate of heat transfer from the air to the fins and from the tubing to the refrigerant. The fins are embossed and louvered to present a greater surface to the passing air. The tubes are also rifled, increasing the surface in contact with the refrigerant. This rifling causes the refrigerant to swirl as it passes through the evaporator, thus ensuring 100 percent contact between the refrigerant liquid and the interior of the evaporator tubes. Condenser The construction of the condenser is similar to that of the evaporator. The physical size of the con denser must be sufficient to dissipate all of the heat of compression and that of the motor as the refrigerant passes through the motor/compressor. It must do this without allowing the temperature and pressure of the refrigerant to exceed acceptable limits. The condenser is one part of the air conditioner that requires periodic maintenance. Accumulated lint and other airborne materials must be cleaned from its surface and from the surface of the fins. 230/208V or 115V plug Capacitor rated for compressor Flared hole for tubing Louvers Fgr. 13 Energy-efficient evaporator tubing fin. Fgr. 14 Cross section of copper tubing showing rifling. Refrigerant filter screen On some room air-conditioning units, a filter screen is used in place of the filter drier. The refrigerant filter is installed in a T-shaped charging connector just ahead of the cap tube. Restrictor tube (capillary tube) The restrictor tube is a refrigerant metering device that determines the amount of high-pressure liquid refrigerant that flows from the con denser to the evaporator. This flow is dependent on the length of the tube as well as its diameter. At normal operating pressures, the feed of refrigerant into the evaporator is fairly constant. Under a heavy heat load, the condenser temperature and pressure increases causing more refrigerant to be forced through the restrictor. Under these conditions, the evaporator pressure and temperature will also increase somewhat. Under low-load conditions, the pressures and temperatures drop. The evaporator may frost heavily or ice up. Automatic expansion valve---The automatic expansion valve is a variable refrigerant metering device. Currently there are two types used on room air conditioners. The automatic expansion valve varies the amount of refrigerant flow to the evaporator maintaining a constant pressure within the evaporator. The constant pressure permits the air conditioner to operate at its de signed evaporator temperature under all operating conditions. This refrigerant control also provides freeze-up protection. As the evaporator pressure and temperature fall, the valve opens, permitting more refrigerant to flow into the evaporator. The increased refrigerant flow raises the suction pressure and temperature to its designed level, eliminating evaporator freeze-up. When the compressor stops, the increase in evaporator pressure causes the valve to close. Fgr. 15 Refrigerant filter location. Fgr. 16 Expansion valve used in 1989 air conditioner. To test the automatic expansion valve, use the following procedure: 1. Disconnect the unit from the electrical power supply. 2. Remove the cabinet shell. 3. Install an adapter or tool so that the compound gauge can be attached to the suction line. 4. Operate the unit, observing the suction pressure. The operating pressure will vary from about 55 to 85 psig, depending on the inside and outside ambient temperatures. After a few minutes of operation with a normal charge of refrigerant, the operating pressure should remain constant as long as the ambient temperatures remain constant.
Fgr. 17 Schematic diagram of a typical multispeed fan motor. Fan motor---Two types of fan motors are used. These are the shaded pole (SF) and the permanent split capacitor (PSC). The motor sizes vary from 1/20 hp to 1/3 hp and are rated for 120-volt ac or 240-volt ac. All motors have a drive shaft at each end for attachment of the evaporator fan and the condenser fan. All fan motors are designed for multispeed operation, either high/low or high/medium/ low. Operating speeds range from 780 rpm to 1850 rpm. Fan motors don’t have start windings, as such, or starting switches. Shaded-pole motors employ a shading coil in the stator to produce the starling torque in the proper direction. When the motor is up to speed, the shading coil has little effect on the operation of the motor. Permanent- split-capacitor motors utilize an auxiliary winding and a low-microfarad electrolytic capacitor to produce the starling torque and rotational direction. When the motor is up to speed, the auxiliary winding and capacitor remain in the circuit. The capacitor is wired in parallel to the main winding, boosting the operating efficiency of the motor. The fan capacitor is often combined with the compressor running capacitor in a single-metal container. The center terminal is common to both capacitors and is shared by both the fan motor lead and the compressor motor lead. Fan speed change is produced in the motor by changing the power connection to the motor at the selector switch. All motors are four-pole motors with a synchronous speed of 1800 rpm. The stator winding is tapped in one or two places to produce the different speeds. The first tap is the main winding connection. Under load, the fan speed will be 1000 to 1500 rpm depending on the model. The second tap and third taps provide medium and low speed, respectively. As more turns of the winding are used, the voltage per turn decreases, reducing both the torque and the speed. Fgr. 18 Evaporator fans. All fan motors are mounted to the bulkhead with three bolts. The evaporator fan shaft extends through the bulkhead. Rubber grommets or flexible mounting legs cushion the motor and reduce sound transmission to the bulkhead. Fan motors are permanently lubricated and need no maintenance. To test the fan motor, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Follow the control panel removal procedure. 3. Check the capacitor using an ohmmeter. See the capacitor test in the Electrical Controls section presented later. 4. If the capacitor checks OK, remove the fan motor leads from the selector switch. Use an ohmmeter to check the motor windings for proper resistance and possible grounds. 5. If the windings check OK, inspect the motor for light bearings or blockage. Fans and Blowers---There are several different types of fans and blower wheels used to move air across the evaporator and condenser of the various models. Evaporator fans operate within a scroll housing. Centrifugal (squirrel cage) blower wheels or radial-flow propeller fans draw air into the center of the scroll and discharge it from the outlet of the scroll into the plenum. Condenser fans are mostly axial-flow propeller fans that draw air through the cabinet-side louvers and blow it through the condenser. Axial-flow fans operate within a plastic shroud. Some have slinger rings around the blade tips to pick up the condensate water. See Fgr. 19. Air conditioners without the side louvers are equipped with radial-flow propeller-type fans that operate in a scroll. The efficiency of any fan is directly related to its position within its housing or shroud. Fgr. 19 Side louver intake condenser fans. Fgr. 20 Scroll condenser fan. The heater on compact models extends across the width of the air outlet grill. On intermediate models, the heater is concentrated in a smaller area and mounted over the evaporator blower outlet. Fgr. 21 Heating element. Heating Element, Thermal Cutout, and Thermal Fuse (Heat/Cool Models Only) An open-coil heating element is used on all heat/cool air conditioners. The heating coil is strung through ring- type porcelain insulators that are supported by a steel frame. The assembly is mounted in the discharge plenum. On compact models, the heater extends across the width of the air outlet grille. On some intermediate models, the heater is concentrated in a smaller area and mounted over the evaporator blower outlet. A metal screen prevents user con tact with the heating element. On heavy-duty and newer intermediate models, the heater is mounted behind the evaporator. Reflective insulation is cemented to the cabinet shell directly above the element. Fgr. 22 Thermal cutout and fuse. The heating element is protected by a thermal cutout connected in series with the heating element. The thermal cutout is mounted on the heater frame. If the fan motor should fail or the air volume become appreciably reduced during heater operation, the thermal cutout will cycle the heater. The contacts of the thermal cutout open at 120°F or 136 ± 5°F and close at 90°F or 98 ± 6°F, depending on the model. Note: The temperature ratings for these devices are given for information only. The actual cutout temperature cannot be accurately tested in the field. If a thermal cutout is suspected of being faulty, it should be replaced. To test the heating element and thermal fuse, use the following procedure: Compact Heat/Cool units are additionally protected by a solid state thermal fuse. Thermal cut-out Intermediate models have the thermal fuse incorporated into the thermal cut-out. 1. Check the wattage and compare the values against the values for that unit. 2. Disconnect the electrical power cord from the electrical outlet. 3. Check the resistance of the heating element. 4. Check the continuity of the thermal fuse. To test the thermal cutout, use the following procedure: 1. Disconnect the electrical power cord from the electrical outlet. 2. Check for continuity. The contacts should be closed at room temperature. ELECTRICAL CONTROLS The following is a description of the electrical controls commonly used on room air-conditioning units. Electronic Controls Fgrs. 24 through 29 illustrate the various electronic controls used on some models of room air-conditioning units. A typical solid-state electronic control system is avail able on one or more models in most capacities. See Fgr. 24. The system features the reliability of solid-state engineering and push-button controls with indicator lights. It incorporates the temperature control selector switch, energy-saving switch, fan speed, and all other feature controls found on conventionally controlled models, plus additional controls and refinements. Fgr. 24 Heating element on heavy-duty and modular intermediate models. Single-sensor type I electronic control (two fan speeds, no filter check, and no frost protection). Fgr. 23 COMPRESSOR; RELAY; REAR VIEW A slide temperature control lets the owner select an actual temperature setting in degrees Fahrenheit. A thermistor sensor is used that makes this control 50 percent more accurate than the thermostat used on conventional models. This reduces the amount of room temperature swing between cycles and provides a more constant level of cooling comfort. The thermistor is positioned on the lower right face of the evaporator by a plastic retainer/spacer. It senses the incoming room air at this point. The power for the compressor and fan motor is controlled through relays mounted on the circuit boards of the control. An improved solid-state energy saver is programmed for an additional 3 minutes of fan run time after the compressor cycles off. This delivers additional cool air to the room, while warming the coil to near room tempera ture. The warm coil permits the temperature control to more accurately sense the true room temperature. An automatic compressor delay circuit eliminates excessive cycling on the overload protector. The compressor won’t operate for 3 to 4 minutes if the unit is turned off and then immediately turned back on. This time delay allows the pressures inside the compressor to equalize. The fan will run during this period, but there will be no cooling. A filter check feature appears on some models. This device lights an indicator lamp after 200 hours of operation. A filter check reset button, when pressed, restarts the electronic counter at zero hours. The owner is instructed to reset the clock after cleaning the filter. (Note: The electronic counter automatically goes to zero hours after a power interruption.) A two-sensor control is used on models when icing of the evaporator is a problem. The extra sensor is attached to either the upper or lower left face of the evaporator. It will sense freeze-up due to operation when the outside temperature is below 70°F or when the air flow is reduced by a clogged filter or other obstruction. This freeze-up control is much more responsive than conventional thermostats sensing both air and evaporator temperature. Further improvements were made on the energy saving feature. See Fgrs. 28 and 29. The control now monitors room air temperature by cycling the fan on for 3 minutes every 15 minutes during the time the compressor is cycled off by the temperature control. This provides improved sensing of changing temperature conditions in the room. A three-speed fan control and a delayed-start/delayed-stop feature are also available on some models. The start-up of the air conditioner can be delayed for up to 14 hours. It can also be operated up to 14 hours and then shut off automatically by an electronic timer. To test the electronic control, use the following procedure: Except for a jumper test of the compressor relay, the electronic control cannot be field-tested by the technician. All components operated by the electronic control, including the power cord wiring, must be tested and proven OK before the electronic control is replaced. Fgr. 25 Single-sensor type I electronic control (two fan speeds, filter check, and no frost protection). REAR VIEW; RELAY Fgr. 26 Dual-sensor type I electronic control (two fan speeds, frost protection, and no filter check Fgr. 27 Dual-sensor type I electronic control (two fan speeds, filter check, and frost protection.) Fgr. 28 Single-sensor type II electronic control (three fan speeds, filter check, and no frost protection). Fgr. 29 Dual-sensor type II electronic control (three fan speeds, filter check, and frost protection). Fgr. 30 Temperature thermistor. To test the compressor relay, use the following procedure: 1. Disconnect the power cord from the electrical supply. 2. Connect a jumper wire with 1-inch female spade connectors to the relay between the COMM and N.O. terminals. 3. Plug in the unit, set the control for HI COOL and the energy saving switch to OFF. Set the temperature control to the coldest setting. If the compressor starts and operates with the jumper, replace the control. 4. If the compressor does not start, remove the jumper and check the compressor capacitor, overload, and wiring. Be aware of the following conditions that could mis lead your diagnosis: The automatic compressor restart delay prevents the compressor from restarting for 3 to 4 minutes to allow the pressure in the sealed system to equalize. When the energy-saving switch is on, the fan will cycle off with the compressor. Models with the filter check counter automatically restart at zero hours after a power interruption. Control Thermostat: Three types of thermostats are used to control the room temperature on conventionally controlled air-conditioning units. Each thermostat consists of a switch to control the compressor, fan, and a temperature-sensitive power element, or actuator, to operate the switch. Freeze protection and temperature thermistor. Gas-filled power element. Gas-filled power element This type of thermostat is sensitive to temperature changes along the entire length of the sensing tube and at the bellows of the power element. The coldest point on the power element becomes the control point for the thermostat. The sensing tube touching the evaporator, or a cold temperature chilling the bellows, will result in short cycling of the compressor. On some low- ampere models, the capillary sensor is coiled next to the thermostat body and is located in the control box. Air from the room is drawn through the control box to activate the thermostat. Liquid-filled power element This type of thermostat has a liquid-filled sensing bulb at the end of the sensing tube. This makes the thermostat sensitive to temperature changes only at the bulb. Freeze protector Fgr. 31 Fgr. 32 Liquid-filled power element. The power element bellows at the switch and the capillary tube (between the bellows and the bulb) are filled with vapor that is boiled out of the liquid in the bulb by the warm room air. The bulb is positioned on the face of the evaporator where it senses the temperature of the incoming room air. It’s mounted in a plastic bulb clamp that clips into the evaporator fins. The clamp also insulates the bulb from the cold evaporator. The thermostat bulb should not touch the evaporator or other cold parts of the air conditioner. Where liquid-filled thermostats are used on heat/cool units, a small heater is attached to the power element at the switch body. This prevents the liquid in the bulb from totally vaporizing under the influence of warm room temperatures, then condensing in the bellows at the switch body when chilled below the outside air temperatures. Coiled capillary---This type of thermostat has a gas- filled power element coiled behind the body of the thermo stat and mounted inside the control housing. Air from the room is drawn through the control housing by the evaporator fan, causing the power element to operate the bellows in the thermostat body. Frost control---Under certain operating conditions, a room air conditioner can freeze up. This means that ice has formed on the cooling coil—even though the unit is set for cooling and is operating, little air is delivered to the room. Freeze-up may occur when the unit is set for cooling and the outside temperature drops below 70°F (particularly when the temperature control is set to the maximum cooling position). Selected model room air conditioners have the thermostat located directly on the cooling coil. At this point it senses frost buildup and turns off the compressor to prevent further frost formation. The fan continues to operate, melting the frost accumulation. The compressor is recycled when the evaporator coil is defrosted. Cool ambient operation---Occasionally, an air conditioner won’t run when the outside temperature is less than 60°F even though the room is warm. The metal in the air conditioner and the body of the thermostat can become so cold that the vapor-actuating medium in the thermostat power element condenses and cannot close the thermostat contacts. The volume of vapor and liquid in the power element bellows is so great, as compared to the volume of liquid remaining in the bulb, that thermostat operation will be controlled by the temperature of the thermostat body and not by the room-side thermostat bulb. Even heating the bulb won’t expand the power element charge enough to operate the switch. Note: If the compressor is forced to run in a very low outside ambient temperature, little cooling, if any, will occur in the room because all the refrigerant will be condensed in the compressor and condenser. The condenser pressure will build very slowly and little refrigerant will circulate through the evaporator. To test the thermostat (cool-only models), use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet front. 3. Remove the control panel to gain access. 4. Remove the wires from the thermostat. 5. Attach an ohmmeter to the thermostat terminals. 6. Warm the sensor—the contacts should close (0 ohms). 7. Cool the sensor (use ice or cold water)—the contacts should open (infinite ohms). To test the control thermostat (heat/cool models), use the following procedure: 1. Disconnect the service cord from the electrical supply. 2. Turn the thermostat to the coldest position and check the continuity across terminals 1 and 2. Continuity should exist. 3. Check the continuity across terminals 2 and 3. No continuity should exist. 4. Turn the thermostat to the warmest position and cool the thermostat bulb. Check the continuity across terminals 2 and 3. Continuity should now exist. 5. With the thermostat bulb still cold, check the continuity across terminals 1 and 2. No continuity should exist. 6. If the thermostat does not check as outlined above, replace the thermostat. (Note: The thermostat bulb must be mounted with the tip up.) Control Thermostat Calibration: The following is a description of the procedure used to calibrate the control thermostat. Operating range of the thermostat---The operating range is the difference between the cutout temperature the coldest thermostat setting and the cutout temperature at the warmest thermostat setting. This difference usually represents an approximately 20 to 21°F temperature change in a 180° rotational movement of the thermostat shaft, or a change equal to approximately 5°F for every 45° rotation. For example, if the thermostat has a cutout temperature between 58 to 64°F at its coldest setting, then the cutout temperature at its warmest setting should be 20 to 21°F warmer, or 78 to 84°F to 79 to 85°F. Operating differential of the thermostat---Determine the cut-in and the cutout temperature of the thermostat by sensing the return-air dry-bulb temperature with an accurate temperature tester. The temperature should be sensed I to finch away from the decorative front, along the lower right half of the air inlet. Average the readings. The difference between the cut-in and the cutout temperature is the operating differential of the thermostat. If this difference is less than or greater than the manufacturer’s recommended differential, the control should be replaced. For example, if the temperature sensed at the cutout on the thermostat is 79°F, then the cut-in should occur when the inlet air temperature increases 2.5 to 5°F. For proper performance, it’s important that the sensing bulb of the thermostat is positioned correctly. On most models, the bulb is positioned I to * inch in front of the evaporator. If the thermostat capillary line or bulb is too close or touching the evaporator, it will sense the coil temperature directly instead of the air temperature, causing the compressor to short cycle. To test the thermostat using a water bath, use the following procedure: Submerge 6 to 8 inches of the capillary line, or the bulb, in a water bath. Set the thermostat at the coldest position. Starting at approximately 75°F, slowly cool the bath and check the cutoff temperature. Raise the bath temperature slowly and check the differential. Repeat the test to confirm the results. Selector Switch: The selector switch is a multi-contact switch that is used to complete selected circuits to the fan motor and the compressor (and to the heater on heat/cool models). Several combinations of fan speed and compressor operation provide for HI and LO cooling, HI and LO fan, Energy Saving, and LO heat (heat/cool models). Medium fan speed is available on some models. Rotary, push-button, and slider switches are used. The rotary and push-button switches have gauged contacts, whereas the slide switches are single pole with one, two, or three positions. To test the selector switch, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet front. 3. Remove the control panel and turn it outward to gain access to the selector switch. 4. Remove the wires from the switch. 5. With an ohmmeter, check the continuity of each position. Example of an externally mounted motor protector. Refer to the unit electrical schematic to identify the terminals involved with each position. Motor Protectors: Two types of motor protectors are used to protect the motors of an air conditioner against damage from electrical and mechanical overload. They are the external and the internal overload. External overload--- The externally mounted motor protector is a bimetal, self-resetting switch. It’s mounted on the compressor shell. It’s actuated by a heater through which all compressor motor current flows. Shell and ambient temperatures have some influence on its operation. Excessive motor current and excessive shell temperature will cause the protector to open. Defective external overload protectors can be replaced. Be sure to use an exact replacement for proper protection of the motor. Internal motor protector---An internal motor protector is used to protect all fan motors and some compressor motors. This device is actuated by excessive motor current and/ or temperature. It’s embedded in the motor windings. It’s connected in series with the common wire to the motor. This application makes it sensitive to the current draw and temperature of both the main and phase windings. When the protector opens from excessive current draw, it will reset automatically after a short time. After repeated operation, caused by prolonged overload or repeated attempts to start, the temperature-sensitive portion of the protector will ex tend the time required to reset. Cycling on the motor protector---When the compressor or fan motor becomes overheated and/or draws too much current, the motor protector trips open and turns off the motor. If this happens repeatedly, the motor is said to be cycling on the motor protector or the overload. Cycling on the motor protector may be caused by… 1. Insufficient air circulation through the condenser. Be certain that the condenser is clean. Shine a light through the fins. Check the entire condenser. 2. Low line voltage. Check the voltage at the compressor terminals while the unit is running and while it’s trying to start. 3. Compressor stalling due to the system pressure not unloading. If, while the air conditioner is operating, the compressor is turned off, then quickly back on, the overload protector contacts will open, breaking the circuit to the compressor common wire. This occurs because the high-side and the low-side refrigerant pressures of the system have not had time to equalize. Approximately 3 minutes are required for the pressures to equalize enough for the compressor to start. The previous condition can also be caused if the room temperature thermostat is short cycling because of too narrow a temperature differential. This condition can also occur because the sensing tube of the thermostat is being pre cooled by touching the evaporator. To test the compressor external motor overload protector, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Remove the compressor terminal cover. 3. Remove the wire connected to the motor protector from the control panel. 4. Check for continuity across the terminals of the overload protector. Continuity should exist at ambient temperature. 5. If the motor protector is open at ambient tempera ture, replace it. To test the compressor internal motor protector, use the following procedure: Refer to the compressor motor test procedure in the Functional Components section presented later in this section. To test the fan motor internal motor protector, use the following procedure: If the fan motor won’t run, make the following test with an ohmmeter to determine if the motor is defective or the internal protector is open. 1. Disconnect the service cord from the electrical power. 2. Remove the control panel cover and rotate it to gain access to the fan motor leads. 3. Disconnect the red and white fan motor leads. Check the motor windings for continuity. 4. If no continuity is found, the protector, or a winding, is open. 5. Allow the fan motor to cool and recheck it. If the circuit through the protector and windings remains open, replace the motor. 6. If continuity is found, check each winding in the motor and compare it to the motor manufacturer’s specifications. Note: If the motor is warm, the resistance of the windings will increase somewhat. A shorted winding will read lower resistance. Running Capacitors: Running capacitors are used on some compressors and some fan motors to increase the efficiency of the motor by improving the power factor. They are connected in series with the phase or auxiliary winding of the motor that operates in parallel with the main or run winding. The running capacitor provides enough electrical phase shift in the phase winding to develop a starting torque. During the initial acceleration of the motor, the phase winding and the running capacitor perform the same function as the start winding on ordinary electric motors. However, when the motor is up to speed, they may remain in the circuit for efficiency and lower cost of operation. Note: The names phase winding, auxiliary winding, and start winding are used interchangeably throughout the trade, as are running winding and main winding. Running capacitors differ from starting capacitors in several ways. They are constructed with a metal case and contain a liquid electrolyte. The microfarad rating is relatively low, but the rated voltage is substantially higher than the line voltage. When both the compressor and the fan motor require running capacitors, both capacitors may be packaged in the same container. These dual capacitors have three terminals. Always replace running capacitors with like type and microfarad rating. Particular attention must be paid to the voltage rating. (Note: A 5-microfarad increase is permissible on compressor run capacitors where periodic or marginal voltage is experienced.) To test the running capacitor, use the following procedure: Caution: An internally shorted capacitor may explode if energized with line voltage. Check it only with an ohmmeter or a capacitor tester. After testing, always discharge the capacitor with a 20,000-ohm, 2-watt resistor placed across the terminals. 1. Disconnect the service cord from the electrical power. 2. Remove the front panel (cabinet shell on slider models), then remove the control panel. 3. Discharge the capacitor. (Note: The best method of discharging a capacitor is with an insulated copper wire in series with the 20,000-ohm, 2-watt resistor. Place this high- resistance jumper across the capacitor terminals.) Fgr. 35 Schematic diagram of PTC relay installation---Start assist device (PTC relay); Compressor 4. Disconnect the capacitor wiring. 5. Connect an ohmmeter across the terminals of the capacitor to be checked: a. If the capacitor is good, the needle should jump toward 0 ohms and quickly drop back to infinity. b. If the needle does not move, the capacitor is open. c. If the needle reads a constant value at or near 0 ohms, the capacitor is shorted. d. If the needle jumps toward zero and falls back to a constant high-resistance value (not infinity), the capacitor has a high-resistance leak. e. Check for a ground from each terminal of the capacitor to the bare metal of the capacitor case. The resistance should be infinite. f. If the resistance is less than infinite, the capacitor is grounded. Replace the capacitor if it’s open, shorted, grounded, or has a high-resistance leak. tor. It, therefore, stays at a high temperature and a high resistance. As long as the compressor runs normally, it has no further effect on the circuit. When the compressor circuit is opened, the thermistor cools down, reverts back to its low resistance, and is ready for the next start. Installing the PTC relay This relay can be mounted in any position. No additional capacitor is needed. To install the PTC relay, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Fasten the mounting bracket to any existing hole in the unit control compartment. 3. Snap the relay into the mounting bracket. Caution: Maintain a 5-inch clearance between the terminal spade connectors and the unit metal parts. 4. Connect one lead between one end of the relay and one side of the run capacitor. (Note: If the unit has a dual capacitor, connect the PTC relay to the high-capacity side.) 5. Connect the other lead between the other end of the relay and the other side of the compressor run capacitor. (Note: The connecting leads are equipped with piggyback spade connectors to ensure available terminals at the compressor capacitor.) PARTS REPLACEMENT OPERATIONS Caution: Review the safe-servicing procedures in the front of this guide before attempting these parts replacement procedures and repairs. Control Replacement (All Models) To replace the control on all models, use the following procedure: 1. Disconnect the service cord from the electrical Start Assist Device: PTC Relay The start assist kit is to be used under conditions of low voltage supply or tight compressor assemblies. The device is essentially a solid-state relay (PTC thermistor) that has a very steep electrical resistance curve relative to its temperature. At room temperature, its resistance is low. At a higher temperature, its resistance increases sharply. This device is connected across the terminals of the compressor run capacitor as shown. At room temperature, its resistance is about 50 ohms. When the electrical power is supplied to the compressor, the capacitor is effectively shorted out of the circuit and the phase winding receives a large current that develops the required starting torque. After approximately k second, the current through the thermistor heats the device and raises its resistance to about 80,000 ohms. At this point, the thermistor has no effect on the circuit and the compressor runs normally with the phase winding operating in series with the run capacitor. Since the device is across the terminals of the capacitor, a slight current trickles through the thermistor power. 2. Follow the control panel removal procedure to gain access to the selector switch, thermostat, solid-state control module, and the exhaust air control. 3. Remove the mounting screws, the electrical and grounding lead connections. Detach the thermostat sensor from the evaporator. 4. Reverse the above procedure to reassemble the unit. Check all wiring connections for tightness. Check all grounding provisions. Solid-State Control Module To remove the solid-state control module, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Remove the control panel. 3. Disconnect the electrical connector from the module. 4. Disconnect the line cord to the module (note the location of the ribbed wire). 5. Disconnect the sensor from its retainer on the evaporator. 6. Remove the four hex-head screws that secure the module to the control panel. 7. Reverse the above procedure to reassemble the unit. Auto-Sweep Motor (Some Models): To service the auto-sweep motor, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Follow the Control Panel Removal procedure to gain access to the auto-sweep motor. 3. Remove the mounting screws, and the electrical and ground lead connections. 4. Reverse the above procedure to reassemble the unit. Check all wiring connections for tightness. Check the safety grounding provisions. Fan Motor (All Models) Servicing the fan motor requires several steps, de pending on the type of chassis involved. A general procedure will be presented here followed by specific requirements for other models. General procedure Slight variations will be encountered on some models. Refer to the specific procedure at such points. 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet shell. 3. Remove the control panel. Disconnect the fan mo tor electrical leads. 4. Remove the screws securing the condenser shroud, or release the tabs holding the shroud. On heavy-duty models, remove the upper half of the shroud. On models with solid side cabinets, leave the shroud attached to the con denser. Fgr. 36 Solid-state control panel removal. Fgr. 37 Auto-sweep motor. Fgr. 38 Positioning condenser for access to fan motor. Compact and standard intermediate models To service these units, use the following procedure: 1. Carefully lift the condenser over the base pan flange. Don’t overstress or kink the refrigeration tubing. See Fgr. 38. 2. Loosen the screw or clamp on the condenser fan hub. Remove the fan shroud. 3. If a blower wheel is used on the evaporator side, proceed to step 11. If a propeller-type evaporator fan is used, proceed to step 4. 4. Remove both the evaporator top cover and the vertical partition between the control box and the evaporator. Fgr. 39 Positioning evaporator for access to fan motor. 5. Remove the screws and brace (top left) securing the evaporator. Carefully lift the evaporator to clear the drain fray and move it to the left to free the right end. Pull the evaporator forward over the edge of the base pan. If possible, work the refrigerant tubing through the bulkhead to avoid bending it. 6. Loosen the clamp on the evaporator fan hub. Proceed to step 8. 7. Loosen the set screw of the clamp on the blower wheel hub. 8. Remove the fan motor ground wire. Free the mo tor leads from the clips and the control box. 9. Remove the fan motor mounting bolts from the condenser side of the bulkhead. Remove the fan motor (the fan or blower wheel will remain in the fan housing). Note: If nuts are found on the evaporator side, it may be necessary to move the evaporator—see steps 4 and 5 above. Fgr. 40 Evaporator blower wheel removal. 10. Reverse the above procedure to reassemble the 9. Reverse the above procedure to reassemble the unit. 11. Rewire the fan motor per the instructions included with the new fan motor. Make sure that the green wire is attached to the new motor. Reseal the wiring and tubing at the bulkhead. Intermediate modular chassis models To service this type of unit, use the following procedure: 1. Remove the screws holding the bulkhead to the base. Lift out the bulkhead with the condenser shroud and the fan motor attached to it. 2. Remove the blower wheel and the condenser fan. Remove the motor. 3. Reverse the above procedure to reassemble the unit. Heavy-duty models To service this type of unit, use the following procedure: 1. Remove the screws holding the bulkhead to the base. Lift out the bulkhead with the fan motor attached to it. 2. Remove the blower wheel and the condenser fan. Remove the motor. 3. Reverse the above procedure to reassemble the unit. Condenser Fan To service the condenser fan, use the following procedures: 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet shell. 3. Remove the screws securing the condenser shroud. Move the shroud toward the bulkhead and pull the locking tabs from the condenser end plate. Note: On models with solid side cabinets, leave the fan shroud attached to the condenser. 4. Carefully lift the condenser over the base pan flange. Position the condenser outside the base. Don’t overstress or kink the refrigerant tubing. 5. On heavy-duty models remove the top half of the condenser shroud. 6. Loosen the set screw or clamp on the condenser fan hub. Remove the fan. 7. Reverse the above procedure to reassemble the unit. Evaporator Tray (All Models) This is a general procedure. Slight variations will be encountered on some models. Evaporator Fan (Blower Wheel) This is a general procedure. Slight variations will be encountered on some models. The procedure at such points will be obvious. 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet shell. 3. Remove the control panel and the evaporator top cover. 4. On intermediate models, remove the screws holding the bulkhead to the base. Release the clips holding the condenser shroud. Lift out the bulkhead, fan motor, and shroud. Remove the blower wheel clamp and the blower wheel. 5. On compact models remove the screws and the brace (top left) securing the evaporator. Remove the vertical partition between the control box and the evaporator. 6. Carefully lift the evaporator to clear the drain tray. Move it to the left to free the right end. Pull the evaporator forward over the edge of the base pan. If possible, work the refrigerant tubing through the bulkhead to avoid bending it. 7. Loosen the clamp on the fan (or blower wheel) hub. Remove the fan housing and the fan. 8. On heavy-duty models, remove the screws holding the bulkhead to the base. Remove the top half of the con denser shroud. Lift out the bulkhead with the motor attached. Remove the clamp and the blower wheel. 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet shell. 3. Remove the control panel and the evaporator top 4. Remove the screws and the brace securing the evaporator. Remove the vertical partition between the control box and the evaporator. 5. Lift the evaporator to clear the tray and move it to the left to free the right end. Pull the evaporator forward over the edge of the base pan. If possible, work the refrigerant tubing through the bulkhead to avoid bending it. Note: For heavy-duty chassis, proceed to step 7. 6. Support the evaporator with a wood block so that the tray can be removed. Slowly pull the tray forward to disconnect it from the drain tube. Proceed to step 8. 7. On heavy-duty chassis: a. Remove the evaporator fan housing. b. Disconnect the drain tube between the evaporator tray and the condenser tray. c. Remove the screws holding the right side of the bulkhead to the base pan. Lift the bulkhead to clear the drain tray. d. Lift the front of the tray, slide it to the left and lift it out. 8. Reverse the above procedure to reassemble the unit. Make certain that the blower wheel does not rub on the evaporator fan housing. Reseal the bulkhead to the base pan and the refrigerant tubing at the bulkhead. Thermal cut-out Fgr. 41 Drain valve, base pan replacement. Condenser Tray (All Models) To service these units, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Remove the unit from the cabinet shell. 3. Remove the screws securing the condenser shroud and the condenser. 4. Carefully lift the condenser over the base pan flange. Position the condenser outside the base. Don’t overstress or kink the refrigerant tubing. 5. Loosen the set screw or the clamp on the condenser fan hub. Remove the fan and the fan shroud. 6. Disconnect the evaporator tray drain hose from the condenser tray. Remove the tray. 7. Reverse the above procedure to reassemble the unit. Base Pan Drain Valve (Heat/Cool Models) To service these components, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet shell. 3. Remove the valve mounting screws to the base pan. 4. Clean the trough area of the base pan. 5. Install the new valve assembly. 6. Reverse the above procedure to reassemble the unit. Fgr. 42 Heat/cool model, thermal fuse, thermal cut out. Thermal Fuse, Thermal Cut-out, and Heating Element (Heat/Cool Models) Note: An external thermal fuse is used on compact models. 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet shell. 3. Remove the protective screen. 4. Remove the heater lead wires. 5. Remove the heater. 6. Use an ohmmeter and check the thermal fuse and/or thermal cutout for continuity. 7. Visually check the heater element for an open coil. 8. Replace the parts as needed. Make sure that all the connections are fight. Make sure that the thermal fuse is positioned away from the heater lead. 9. Reverse the above procedure to reassemble the unit. Exhaust Air Door Note: On compact and heavy-duty cabinets, the shell must be removed to make repairs to the exhaust air door. The actuating cable and/or the control lever replacement or adjustment can be performed through the discharge Thermal cut-out Fgr. 43 Side-mounted type (reciprocating compressor). Fgr. 44 Top-mounted type (rotary compressor)---air plenum, except on blow-through models. On blow- through models, the exhaust door is located behind the evaporator coil. The exhaust air door control knob and/or cable can be serviced by removing the control panel. Compressor Motor Protector (External Protector Only) To service these units, use the following procedure (See Fgr. 43): 1. Disconnect the service cord from the electrical power. 2. Remove the cabinet shell. 3. Remove the compressor retainer and terminal cover. 4. Remove the protector lead from the compressor terminal. 5. Remove the remaining electrical lead from the protector terminal. 6. Remove the protector. 7. Reverse the above procedure to reassemble the unit. Top-mounted type (rotary compressor) To service these components, use the following procedure: 1. Disconnect the service cord from the electrical power. 2. Remove the chassis from the cabinet shell. 3. Remove the compressor retainer and terminal cover. 4. Remove the protector lead from the compressor terminal. 5. Remove the remaining lead from the protector terminal. 6. Remove the protector. 7. Reverse the above procedure to reassemble the unit. Make certain that all the electrical connections are tight. Adjusting the Condenser Fan Blade (Intermediate Modular Chassis) To adjust the condenser fan blade on intermediate modular chassis, remove the unit from the cabinet shell. Locate a round plug on top of the condenser shroud. See Fgr. 45. Cut the membrane on each side of the plug and push on one side to roll the plug out of the opening. Insert a screwdriver blade through the opening and loosen the clamp on the condenser fan blade. After adjusting the blade, tighten the clamp and cover the hole with a piece of two-inch-wide duct tape. Fgr. 45 Adjusting the condenser fan blade. TROUBLESHOOTING Caution: Review the safe-servicing procedures in the front of this guide before attempting these diagnosis and repair procedures. Air-Conditioner Voltage Limits 4. Blown fuses. 5. Premature failure of the compressor or the fan motor. 6. Noticeable dimming of lights when the air conditioner is running. 7. Evaporator icing. Low voltage may reduce the fan speed resulting in an inadequate air flow over the evaporator, thereby allowing it to ice up. Often, low voltage can be attributed to the use of extension cords or an inadequately wired circuit. However, low voltage into the building and loose fuses or connections in the power supply should not be overlooked. Low voltage may also be a general condition in the area (a responsibility of the power company). All units will start and run on the minimum voltage stated on their nameplate and they will perform satisfactorily if the voltage remains constant. Low voltage caused by defective wiring won’t remain constant under a load. Testing for low voltage should be done with a reliable voltmeter with a capacity to measure the required voltage. Measurements should be taken at the electrical service en trance and at the electrical outlet serving the air conditioner. Readings should be taken with the unit off, while the unit is starting, and again while the unit is running. The lowest reading should not drop below the lowest value listed on the unit nameplate. Nameplate | Rating 120 volts ac 240 volts ac 208/240 volts ac Minimum 103.5 volts ac 207 volts ac 197.5 volts ac Maximum 126.5 volts ac 253 volts ac 253 volts ac High Voltage: High voltage can l as equally troublesome by causing motors to overheat, cycle on their protectors, or break down electrically. This problem can be solved by the power company. Low Voltage: Low voltage is a common cause of trouble in the operation of any room air conditioner. It becomes doubly important, because of the motor size, that the service technician checks the voltages when servicing room air conditioners. Improper voltage may result in one or more of the following complaints: 1. Unit won’t start. 2. Compressor motor cycling on the motor protector. 3. Premature failure of the motor protector. Electronic Control This type of control is not repairable. If any component on the control is defective, the entire control must be re placed. Important note: Repair or replace any malfunctioning line voltage component before testing or replacing the electronic control. Don’t assume a service problem is directly caused by the electronic control system. A line voltage component (including the power cord and wiring) that has opened, shorted, grounded, or otherwise malfunctioned may have created the service problem. Home top of page |