Refrigerator coil defrost heater


Old 05-20-05, 06:14 AM
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Join Date: Oct 2002
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Refrigerator coil defrost heater

The coil in my refrigerator iced up solid this week. I found a broken wire on the thermostat switch which controls the defrost heater. After fixing the wire I shorted out (bypassed) the switch to make sure the heater worked. The heater would not come on with the switch shorted. I then verified that the heater worked by powering it from a separate source. I figured that the heater circuit might only be powered when the compressor is off. I tried turning the compressor off by turning down the thermostat but the heater circuit did not energize. Is it likely that the heater circuit is only powered at certain times? Is there a way to verify that the heater circuit is working?
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Old 05-20-05, 10:31 AM
Join Date: Sep 2001
Location: Yorktown, VA
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"Is it likely that the heater circuit is only powered at certain times?"

Yes. A defrost timer is responsible for that task. At certain intervals, it turns the compressor off and the defrost heater on. The heater stays on until thermostat (the one you found the bad connection on) is satisfied or the the defrost timer switches back to the refrigeration mode.

Hopefully, one of the other regulars with more recent experience may be able to help you locate the timer. They are in different places on different models.

Good luck,
Old 05-20-05, 05:33 PM
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defrost heater

Defrost heaters (depending on the model) are located at the bottom left hand corner of the refrigerator or on some models inside the refrigerator. Now, depending on the age of the refrigerator, some older ones use the mechanical type of timer while others use a circuit board mounted inside. To know which one you have is impossible from my position. If you do find it down at the bottom of the fridge, take a flat blade screwdriver and turn the knotch clockwise until you hear a click and the refrigerator shuts down. Once that is accomplished then power will be sent to the defrost circuit. If you find you have a timer that is on a circuit board then the only way to make it go into defrost is through a special set of instructions usually located on the tech sheet tucked away somewhere at the bottom of the fridge. If icing is your problem then there are three possibilities. Defrost terminator(also known as thermostat) defrost heater, or the defrost timer. IF both terminator and heater check out ok, then its usually the timer.
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