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THE SWITCH The switch is a mechanical device used for directing and controlling the flow of cur rent in a circuit. Simply put, the switch can be used for turning a component on or off (Fig. __2). Internally, the switch has a set of contacts that close, allowing the current to pass; and when opened, forbidding the current to flow through it. Built into the switch, a linkage mechanism actuates these contacts inside of the closed housing. (__3) The exploded view of a switch a linkage mechanism actuates these contacts inside of the closed housing __1 A Typical electric range parts identification. Top burner elements; Indicator lights; Thermostats; Oven and panel light bulbs; Bake and broil elements; Broiler pans; Selector switches; Infinite (top element) switches; Self-cleaning oven sensor; Portable models; Upper rack; Lower rack; Float (overflow protection); Detergent dispenser; Control panel; Filter; Heating element coupler __1 B Typical dishwasher parts identification. Bushing and seal kits; Brake drum — Transmission components; Solenoids; Power cord; Model and serial number plate; Lower spray arm; Rinse agent dispenser; Switches; Timer and Agitators components; Agitator blocks; Water valves; Drive belts; pumps; Pump hose __1C Typical automatic washer parts identification. Timers; Drum support bearings; Elements and igniter components; Drum belts; Thermostats; Idler pulley; Support rollers and glides __1 D Typical automatic dryer parts identification. Switch (closed) __2 The wiring diagram illustrates a switch in the closed position. If the switch is closed, the light and motor are on. If the switch is open, the light and motor are off. Switches come in a wide range of sizes and shapes, and can be used in many different types of applications (Fig. __4). They have a voltage and amperage rating marked on the switch, or on the mounting bracket, for the type of service the individual switch was designed to do. The switch housing is usually marked with the terminal identification numbers that correspond to the wiring diagram. It identifies the contacts by number, normally open (NO) contacts, normally closed (NC) contacts, or common (COM). Internally, the switch can house many contact points for controlling more than one circuit. When suspecting a switch failure, remember that there are only three problems that can happen to a switch: • The contacts of the switch might not make contact. This is known as an open switch. • The switch’s contacts might not open, causing a shorted switch. • The mechanism that actuates the contacts might fail. This is a defective switch. When these problems arise, the switches are not repairable, and they should be replaced with a duplicate of the original. Pressure switch The pressure switch is a specialty switch, with a similar operation to those above, but with one important exception. The pressure switch is actuated by a diaphragm that is responsive to pressure changes (Fig. __5). This switch can be found in washing machines and in dishwashers, and it operates as a water level control. Other uses include: furnaces, gas heaters, computers, vending machines, sump pumps, and other low pressure applications. The pressure switch is not serviceable, and should be re placed with a duplicate of the original. Thermostat The thermostat operates a switch. It is actuated by a change in temperature. The two most common heat-sensing methods, used in appliances, are the bimetal and the expansion types (Fig. __6). The bimetal type (Fig. __7) consists of two dissimilar metals combined together as one. Any change in temperature will cause it to deflect, actuating the switch contacts. When the bimetal cools, the reverse action takes place. __4 This is a sample of the many types of switches used in major appliances. NC contacts; Mounting hole The expansion t (Fig. __8) uses a liquid in a tube that is attached to bellows. The liquid will convert to a gas when it is heated, and will travel up the tube to the bellows. This causes the bellows to expand, thus actuating the switch contacts. When the gas cools, the reverse action occurs. Thermostats are used in applications as diverse as gas and electric ranges, automatic dryers, irons, waterbeds, spas, and in heating and refrigeration units. __5 The pressure switch construction. __6 A bimetal and expansion-type thermostat. Electromechanical timer. Although the timer is the most complex component in the appliance, don’t assume that is the malfunctioning part. Check all of the other components associated with the symptoms, as described by the customer. Electromechanical timers are utilized for controlling performance in automatic washers, automatic dryers, and dishwashers. Most timers are not serviceable, and should be replaced with a duplicate of the original. To dome on washer outer tub; Projection arm; bar; Bimetal type; Auxiliary heater; Bimetal element; Switch contacts The timer assembly is driven by a synchronous motor, in incremental advances. It controls and sequences the numerous steps and functions involved in each cycle of an appliance (Fig. __9). The timer directs the on and off times of the components in an electrical circuit. The timer consists of three components assembled into one unit. The components are the motor, the escapement, and the cam switches (Fig. __10). __7 The bimetal thermostat construction. __8 Temperature-control construction. Overload; Switch contacts; Temperature control; Dust cover __9 An electromechanical timer Timer Switch locating boss; Motor mounting screws Tab “B” #2 switch; Rear view; Dust cover; Dust cover removed; Escapement; Motor; Cam switches __10 The timer components: motor escapement, and cam switches. The motor The motor is a synchronous motor, geared to drive the escapement. In Figs. __9 and __10, the motor is mounted on the timer assembly. These are specially designed motors, whose speed is controlled by the 60-cycle period of the current, rather than the fluctuating supply voltage. The cam switches The number of switch contacts, and cams, varies with the number of functions an appliance performs. Some of the switches perform two or more functions (Fig. __11). The particular shape of the cam varies with the number of switch contacts that it controls, and the length of time each switch contact opens and closes (Fig. __12). A single metal strip, called a cam follower (Fig. __11), is anchored to each cam switch arm. As the cam turns, this metal strip follows the contour of the circumference of the cam, causing the cam switch to open, or close, at the proper time. Outer contact, Neutral section, Cam follower, Inner contact, Cam, Inner contact, Cut out, Raised portion, Cam follower __11 The timer cam and switch contacts’ construction. The escapement The escapement is a spring-controlled mechanism that limits the cam shaft rotation to a set number of degrees in each increment (Fig. __10). The cam follower moves rapidly to ensure a snap action of the switch contacts, and also to prevent any arcing of the points. Not all timers have an escapement. For example, some dryer timers, and all defrost and electronic timers, have no escapement. Relays A relay is an electrically operated switch. It contains an electromagnet, with a fixed coil and a movable armature, that actuates a set of contacts to open and close electric circuits (Fig. __13). Relays have heavy-duty switching contacts, and they are used to operate larger components, such as motors and compressors. The most common failures of relays are: Outer contact • Open relay coil • Burned switch contacts • Armature not actuating the contacts. A broken relay is not serviceable, and should be replaced with a duplicate of the original. __12 This illustration shows how a switch contact opens and closes on the cam. __13. The relay construction. A solenoid is a device used to convert electrical energy into mechanical energy (Fig. __14). When a solenoid is energized, it acts like an electromagnet, positioned to move a pre-designated metal object. The work done by the moving core makes the solenoid useful in appliances. Some solenoids are equipped with a free-moving armature or plunger. Common failures of a solenoid are: • Open coil. • Shorted coil. • Jammed armature. A solenoid is not a serviceable part, and should be replaced with a duplicate of the original. These devices are manufactured in a variety of designs for various load force and operational requirements. Solenoids are found in automatic washers and dryers, gas and electric ranges, automatic dishwashers, refrigerators, freezers, automatic ice machines, and in heating and air conditioning units. Coil, Armature, Relay SOLENOIDS __14 The solenoid coil and plunger When the coil is activated, the plunger will be drawn to the center of the magnetic field. WATER VALVES The water inlet valve controls the flow of water into an appliance, and is solenoid- operated (Fig. __15). When it is energized, water in the supply line will pass through the valve body and into the appliance. Listed below are some different types of water inlet valves that are used on appliances: • Single water inlet valve (Fig. __16); used on dishwashers, ice makers, refrigerators, undercounter ice machines. • Dual water inlet valve (Fig. __17); used on washing machines, refrigerators, icemakers. Some dishwasher models also use dual water inlet valves. The inlet side of the valve has a fine mesh screen to prevent foreign matter from entering the valve. Some water valves also have a “water hammer” suppression feature built into them. __15. The water valve construction. Outlet __16 The single water valves are just some of the different types available that are used in major appliances. __17 These dual water valves are designed for dual water-inlet connections. Drain valves (Fig. __18) are used on some dishwasher and washing machine models to control the drainage of the water in the tub, and its expulsion into the sewage system of the residence. The water valve should not be serviced. Replace it with a duplicate of the original. The two major assemblies that form an electric motor are the rotor and the stator (Fig. __19). The rotor is made up of the shaft, rotor core, and (usually) a fan. The stator is formed from steel laminations, stacked and fastened together so that the notches form a continuous lengthwise slot on the inside diameter. Insulation is placed so as to line the slots; and then coils, wound with many turns of wire, are inserted into the slots to form a circuit. The wound stator laminations are pressed into, or otherwise assembled within, a cylindrical steel frame to form the stator (Fig. __20). The end bells, or covers, are then placed on each end of the motor. One important function of the end bells is to center the rotor, or armature, accurately within the stator to maintain a constant air gap between the stationary and moving cores (Figs. __19 and __21). These coils of wire are wound in a variety of designs, depending upon the electrical makeup of the motor. They provide two or more paths for current to flow through the stator windings. When the coils have two centers, they form a two-pole motor; when they have four centers, they form a four-pole motor. In short, the number of coil centers determines the number of poles that a motor has (Fig. __22). Thermal protection in a motor is provided by a temperature-sensitive element, which activates a switch. This switch will stop the motor if the motor reaches the pre-set temperature limit. The thermal protector in a motor is a non-replaceable part, __18 The drain water valves. MOTORS __19 The stator and rotor; Stator; Counter weight __20 Stator and rotor construction. __21 End bells position motor shaft in center of stator and the motor will have to be replaced as a complete component. There are two types of thermal protection switches: • Automatic reset It automatically resets the switch, when the temperature has been reduced. • Manual reset It has a small reset pushbutton on the motor, on the opposite end from the shaft. On the following list are several types of motors that are used for different types of applications: • Synchronous motors are permanent magnet timing motors, used in automatic ice cube makers, water softeners, and humidifiers. Also, they are integral to timers for automatic washers, automatic dryers, and dishwashers. • Shaded pole motors are used as continuous duty motors, with limited or adjustable speeds. They are used for small fans and clocks. • Split phase motors are used as continuous duty motors, with fixed speeds. Some are: automatic washer and dryer drive motors. • Capacitor start motors are similar to the split phase motors, and they are used in hard-to-start applications such as compressors and pumps. • Permanent split capacitor motors are used in a variety of direct-drive air- moving applications; for example, air conditioner fans. • Three phase motors are used in industrial, or large commercial, applications where three-phase power is available. • Multi-speed, split phase motors are used in fans, automatic dryers, automatic washers, and many other appliances. Figure __23 illustrates some of these motors. Appliance motors are not repairable, and they should be replaced with a duplicate of the original. CAPACITORS __22 2-pole motor/4-pole motor A capacitor is a device that stores electricity to provide an electrical boost for motor starting (Fig. __24). Most high-torque motors need a capacitor connected in series with the start winding to produce the desired rotation, under a heavy starting load. There are two types of capacitors: Two-pole stator motor. 1/2 Cycle Other 1/2 cycle. Four-pole stator motor. • Start capacitor--This type of capacitor is usually connected into the circuit between the start relay and the start winding terminal of the motor. Start capacitors are used for intermittent operation (on and off operation). • Run capacitor--The run capacitor is also in the start winding circuit, but it stays in operation while the motor is running (continuous operation). The purpose of the run capacitor is to improve motor efficiency during operation. Capacitors are rated by voltage, and by their capacitance value in microfarads. This rating is stamped on the side of the capacitor. A capacitor must be accurately sized to the motor and the motor load. Both run and start capacitors can be tested by means of an ohmmeter. __23 Motors are available in different sizes and shapes. HEATING ELEMENTS Most heating elements are made with a nickel-chromium wire having both tensile strength and high resistance to current flow. The resistance and voltage can be measured with a multimeter to verify if the element is functioning properly. Heating elements are available in many sizes and shapes (Fig. __25). They are used for: • Cooking food • Heating air for drying clothes • Heating water to wash clothes, dishes, etc. • Environmental heating. __24 A. The capacitor is rated by voltage and by capacitance (in microfarads). B. This built-in disconnect device is also known as a fail-safe. __25 Heating elements. Heating elements are not repairable, and they should be replaced with a duplicate of the original. MECHANICAL LINKAGES The mechanical linkages are those devices (connecting rods, gears, cams, belts, levers, pulleys, etc.) that are used on appliances in order to transfer mechanical energy from one point to another point. Figure __26, is an excellent example, the automatic ice maker. Some other examples are: • In the automatic dryer, the motor is turning a pulley, which moves a belt, which turns the drum. • In the automatic washing machine, the motor turns a pulley, which moves the belt, that turns the transmission gears, that performs the agitation or spin cycles. • In the automatic icemaker, the timer gear turns the drive gear, which moves the cam, that actuates the switches, and rotates the ice ejector. Normal; Fail-safe mode; Brass drive gear; Ice maker weigh switch shaft; Shaft ice level control; Gear ice maker drive __26 The ice maker a perfect example of mechanical linkages in use. WIRES The wiring, which interconnects between the different components in an appliance, is the highway that allows current to flow from point A to point B. Copper and aluminum are the most common types of wires that are used in appliances. They are available as solid or stranded. Wires are enclosed in an insulating sleeve, which might be rubber, cotton, or one of the many plastics. Wires are joined together, or to the components, by: • Solderless wire connectors • Solderless wire terminal connectors • Solderless multiple pin plug connectors • Soldering Never join copper and aluminum wires together, because the two dissimilar metals will corrode and interrupt the flow of current. The standard wire-gauge sizes for copper wire are listed in Table __i. As the gauge size increases from 1 to 20, the diameter decreases and the amperage capacity (ampacity) will decrease also (Table __2). Table __1. Copper wire table; Gage no.; Diameter, mil. ; Circular-mil area ; Ohms per 1000 ft. of copper wire at 25° C*; Appliance selection, service, installation, and preventive maintenance procedures
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