Ultimate Fix-It-Yourself Manual: Large appliances--Refrigerators / cycle-defrost

In a typical cycle-defrost refrigerator, refrigerant is pumped through evaporator plates in the back of the refrigerator compartment and in the back, top, and bottom of the freezer. The temperature is controlled by a thermostat.

In the refrigerator compartment, a defrost heater connected to the plate cycles on after each running cycle to melt any frost. (On models without a heater, the thermostat lets the temperature rise to a few degrees above freezing to melt the frost.) A tube carries the melted frost to the drain pan under the refrigerator. The freezer is defrosted manually by turning the thermostat dial to the Defrost or Off position.

Don’t touch the evaporator plates. Skin oils and acids can cause spots that cause an excessive buildup of frost. To remove such spots, wash them with hot water and an automatic dishwasher detergent labeled safe for aluminum.

Testing and replacing the heater:

1. To test defrost heater, disconnect its leads from thermostat. With VOM on RX1, clip probes to leads. Look for reading between 200 and 1,000 ohms; a much higher reading or infinity indicates defective heater.

2. To replace defrost heater, pry off its cover (Step 3, below). Untape and cut its leads. Connect new leads with crimp-on in-line wire connectors. Fill them with silicone sealer and cover securely with tape.

Testing and replacing the thermostat:

1. Unplug refrigerator. To access thermostat, pull or pry dial off shaft. Then unscrew thermostat and gently pull it out of wall. Take extra care not to make a sharp bend in the metal capillary sensing tube attached to thermostat.

2. Test thermostat when refrigerator is near room temperature. Take oft leads and turn thermostat to Off position. With VOM on RX1, clip probes to terminals. Look for infinity reading. Turn to coldest setting; look for zero.

3. To replace thermostat, pry off heater cover. Then loosen (don’t remove) screws that secure the clamps that holds the thermostat sensing tube bulb.

4. Tape a string to sensing tube and pull tube out of wall. Tape string to new thermostat tube and use it to guide tube into place. Make sure to replace plastic sleeve, if any, on sensing tube, and be careful not to kink the tube.

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