above: Anatomy of a romom A/C: Compressor terminal box; Evaporator fan; Fan shroud; compressor fan; Bulkhead or divider. Note: Detail or repair and disassembly may vary, depending on appliance model, It your air conditioner differs markedly from this one, see Appliance repair basics.
An air conditioner (A/C or AC) circulates refrigerant in a continuous loop through two sets of coils. In the unit’s indoor half, the refrigerant flows through the evaporator coil as a heat-absorbing gas. In the condenser coils outdoors, the gas is compressed and changed into a liquid causing it to give off heat. Fins on the coils and fans maximize the heat transfer. A thermostat controls the operation.
Air-conditioner capacity is measured in Btu’s (British thermal units) per hour. The capacity should match the room size (see Quick formulas). A unit that’s too small cools poorly and runs too long, which may damage it. unit that’s too large cools quickly with out removing enough humidity.
If a unit smells bad, unclog the drain hole, if any, and pour in 1 teaspoon of household ammonia. Clean the evaporator fins with automotive degreaser c refrigeration coil cleaner; make sure the product is marked safe for use on aluminum. Wash the drain pan with disinfectant. If the odor persists, have the unit steam-cleaned at an auto repair shop.
To prevent indoor dripping, slope unit toward the outside by a reading of a quarter bubble on a spirit level.
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QUICK FORMULAS
What size air conditioner do you need (in Btu’s)?
1. Find room volume. Multiply (in feet): length x width x height
2. Multiply result by factor corresponding to direction most exposed wall faces: 16 north, 17 east, 18 south, 20 west.
3. Divide result by factor corresponding to the quality of your home’s insulation: 4 poor, 5 good, 6 excellent
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!!! FOR YOUR SAFETY!!!
Unplug an air conditioner---before opening the control panel or removing the cabinet.
Discharge the capacitor---before working on any of the parts inside an air conditioner.
Test for adequate voltage before plugging in art air conditioner. If a unit’s compressor doesn’t work or cuts on and off, the outlet voltage may be too low.
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Troubleshooting:
| SYMPTOM | POSSIBLE CAUSE | SOLUTION |
Won’t run Doesn’t cool; fan runs Fan doesn’t run Cools poorly Cycles on and off often Noisy Frosts up |
Power off at outlet or faulty power cord Faulty selector switch Dust-clogged filter or evaporator fins Faulty thermostat or selector switch Faulty compressor overload protector Faulty capacitor Dust-clogged condenser fins Faulty compressor Faulty selector switch Faulty capacitor Motor hums: loose or obstructed fan Motor hums: binding motor shaft or bearing No motor hum: faulty fan motor Outdoor air leaking into room Dust-clogged filter or evaporator fins Clogged or blocked condenser Ventilator stuck open or broken Loss of refrigerant Thermostat too high Overload protector activated Clogged or blocked condenser Thermostat sensor bulb touching coils Faulty capacitor Clicking sound: fan hitting housing or tubes Knocking at shutoff: faulty compressor spring Vibrating screws or trim Tubes hitting cabinet Loose fan Pinging sound: condensate hitting condenser Whistling sound: bent evaporator fins Low outdoor temperature Dust-clogged filter or evaporator fins Loose or binding fan; slow motor |
See General troubleshooting Test and replace Clean Test and replace Test and replace Test and replace Clean Test and have serviced Test and replace Test and replace Tighten or remove obstruction Oil motor Test and replace Seal air gaps around air conditioner. Clean. Clean or clear obstruction. ‘ Spray lubricant on sticking parts; replace broken ones. Have serviced. Lower setting. Shut off unit; wait 20 mm. before restarting. Clean or clear obstruction. Put bulb back in supports. Test and replace. Reposition unit slightly; gently shift tubes. Seldom serious; ignore or have compressor replaced. Tighten screws; shim loose trim. Gently shift tubes. Tighten. Ignore; this is how unit evaporates condensate. Straighten. Don’t run unit when it’s below 60-degr. F outside. Clean. Check fans; test motor. |
[Degree of difficulty: Simple --- Average 4 --- Complex • Volt-ohm meter required: I]
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Gaining access:
To remove grille, unplug unit; remove grille screws or press against edges of grille with a putty knife to release clips. On many models, releasing hidden tabs on top edge lets you lift grille up and away. If necessary, consult the owner’s manual to locate the tabs. Be careful not to dislodge the thermostat sensor bulb.
To reach controls and power cord on many models, remove panel beneath switch knobs. First unplug the unit; then remove the grille and gently pry or pull the knobs from their shafts. Lift off faceplate and unscrew the panel. CAUTION: Discharge the capacitor before testing or working on controls.
To open a large unit, unplug the power cord, remove the front grille, pull the chassis forward, and place a support under the front edge. Most interior parts can be reached with chassis only partly removed from cabinet. To remove the chassis completely, get a helper; two people are needed to carry it safely.
To open a small unit, unplug the power cord and lift unit from the window. Grasp sides securely while a helper raises sash; other wise air conditioner may fall. Set unit on a work surface and remove the grille. Then remove the screws along the lower edges and lift off the cabinet.
Fans and fan motor:
To reach the fans or fan motor, unplug the air conditioner and open the cabinet (see: Gaining access). Rotate the fan until you seethe screw that secures it to the motor shaft. On a plastic fan, the screw is one clamp around the fan’s hub, it’s on the hub itself on a metal fan.
If a fan is hard to turn, the motor may need oil. Or it may have vibrated out of position. Temporarily loosen the motor’s mounting nuts and reposition it until the fan rotates freely.
If the motor runs poorly or not at all, trace its leads back to the control panel. Label each lead and remove it from its terminal. With a VOM on RX1, clip one probe to the common (often white) lead and probe each of the other leads in turn. Look for a low ohms reading at each test. If a reading is high, replace the motor or test it more fully (see Faulty split-phase motor).
CAUTION: Before testing or removing the motor, discharge the capacitor.
Motor powers evaporator and condenser fans.
To secure condenser fan blades, tighten screw on metal clamp around hub; there’s usually an access hole. (Ca metal blades, use hex key to tighten setscrew against shaft’s flat side.)
Tighten evaporator blower fan by inserting long screwdriver into access hole or gap in blades to reach screw on metal clamp. (On metal blades, use long hex key to tighten setscrew.)
To replace a motor, carefully unscrew and shift condenser coils out of the way. Remove fan shroud and both fans. Trace motor leads to terminals on control panel, note locations, and disconnect them.
Unscrew mounting bolts and pull out motor. If motor leads follow an intricate path, tie strings to the ends and pull the strings through the unit as a guide for rethreading new leads.
Compressor:
If the compressor doesn’t work, the unit won’t cool. Open the terminal box on the compressor and test its motor terminals and the overload protector (usually located inside the box). If the motor and protector are 0 check for a defective thermostat or capacitor. Suspect a shorted capacitor if the compressor operates briefly after a long interruption, then stops.
CAUTION: Before testing a compressor, unplug the unit; make sure that 20 minutes have passed since you last ran it. Discharge the capacitor.
To test compressor motor, pry off clamp holding terminal box cover, and take off leads from motor terminals. With VOM on RX1, test all possible pairings of the three terminals for continuity. Look for a reading of low ohms on each pair. Then test for a ground fault: With VOM on RX100, touch one probe to bare metal on compressor or its refrigerant line; touch second probe to each terminal in turn. Reading should not waver from infinity. If motor fails any test, have compressor replaced.
Check overload protector, and replace if it has a cracked housing or burned terminals. To test it, detach the lead and set VOM on RX1. Check for continuity by probing both terminals. Look for a zero reading; replace if reading is high or infinity. If the overload protector is internal, you won’t be able to inspect or test it. Suspect a faulty internal protector if a test of the motor terminals results in an infinity or high ohms reading.
Switch and thermostat:
The selector switch controls the compressor end fan speeds. It’s also linked to the thermostat, which monitors room temperature with its sensor bulb on the evaporator coils. Before testing a troublesome rotary or push-button selector switch, try spraying it with electrical contact cleaner; the spray alone may clear up the problem. Electronic touch- pad controls are difficult to test and, if faulty, usually require replacement. Unplug the unit before opening the control panel. Energy- saver switch; Selector switch; Thermostat.
Test a rotary selector switch with VOM on RX1. Clip a probe to COM terminal. Setting knob in one position at a time, probe other terminals in turn as shown in Testing a selector switch.
Test a push-button switch with VOM on RX1. Clip one probe to COM terminal. Pressing one button at a time, probe each of the other terminals as shown in Testing a selector switch.
Test thermostat at room temperature with control switch on coldest setting. Remove leads and set VOM on RX1. Probe terminals. Look for reading of zero; replace if reading is infinity or high ohms.
When replacing faulty thermostat, thread tube along the same path as the original. Mount bulb in same position, using original clips or plastic tube or new mounts supplied with replacement.
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Clean filter at least once a month during cooling season. Wash foam and metal mesh filters in soapy water. Rinse, let dry; reinstall. Replace disposable filters with same type.
Vacuum evaporator fins when changing filter. To clean clogged evaporator or condenser fins, spray with coil cleaner; flush with water. Straighten bent tins with fin comb.
Clear clogged drain tube or hole in partition with wire. To kill organisms that cause sludge, pour in (or drip in with old medicine dropper) 1 tsp. of household ammonia.
Lubricate fan motor every 6 mo. if motor has oil ports—they’re usually plugged with screws or caps. Put no more than 5 drops of SAE 20 non-detergent motor oil in a port.
Cover air conditioner before winter unless you can remove and store it. It’s also a good time to clean and straighten condenser fins and repair rust on cabinet and drain pan.
Here are some more tips on keeping your air conditioner running efficiently and safely:
Keep potential obstructions like curtains, furniture, and houseplants 2 feet away from the unit. Frosted coils also block airflow; don’t run a unit when it’s below 60°F outside.
On very hot days, turn on the unit early in the morning for maximum efficiency, and let it run continuously. Water dripping from the drain pan of an air conditioner during periods of high humidity is normal.
After turning off an air conditioner, wait 5 minutes before restarting it, to lessen strain on the compressor. Turn off a unit immediately if the fan motor doesn’t run.
