Tip & How-To about Refrigerators

How it works: Defrost circuit on a modern refrigerator

Whether your refrigerator works with a fancy computer program to determine defrost or has a plain Jane tried and true timer for defrost, the defrost heater and termination thermostat is the same in both. Any self defrosting ice box has 3 components, A timer or electronic device to commence defrost operation, a heater to warm the coils and melt the frost, and a defrost heater termination thermostat to shut down the the heater after the temp has warmed enough to do the job. The typical defrost cycle lasts from 21 mins on a conventional timer to 40 mins on electronic monitored ice box's. Checking the heater is easy enough, if it has continuity it is ok. checking a defrost thermostat is a little more tricky. It will be open if it is above 50f where you are testing. The design is 25f it closes and allows power to the heater and at 50f it opens and shuts down power to the element. because the element cannot remain on for the entire cycle. Here is a video i recently put together to show what to check in a defrost circuit, While all ice box's are diff in size and specs they all work the same.

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The ice maker stoped working about a week ago. And now neither the fridge or freezer are working.

The first thing I would look at is the area around the compressor. themobilian_280.jpg
I want the fan to be running down there. I also need the coils to be cleaned so they don't restrict the air flow. I want the compressor to be warm to the touch but not hot and not cold. If the fan is running and the coils are clean I want to take a closer look at the compressor. The relay on these will simply fall apart over time.themobilian_281.jpg
I want to make sure I am getting power to the compressor. No power down there? We go upstairs to the control. I want to first take a look at the defrost timer or electronic defrost control. I want to make sure the timer is in compressor run mode and is not hung in defrost mode. themobilian_282.jpgI want to check an automatic defrost control for corrosion at the connection. Sometimes yanking it out of its socket will make a better connection and all will be well again.themobilian_283.jpg
If all of that is fine and the compressor is running I want to take a look at the evaporation coils. If they are iced over then I know I either have a bad defrost heater or defrost heater termination thermostat. themobilian_284.jpg
Why do we need a termination thermostat? It activates the heater when the temp in the freezer is below 25f AND the defrost timer or control calls for defrost. You see the defrost heater and terminator are still same whether you have the old tried and true defrost timer or the fancy smancy electronics. The defrost termination thermostat kills the power to the heater when the temp reachs 50f. Why is this important? Because the defrost mode stay on for 20 minutes or longer. If we leave that heater on that long the ice box would be damaged or destroyed. The ice buildup resulted from a failed defrost takes a week or longerthemobilian_285.jpgthemobilian_286.jpg I have more Info Here

I have service manuals and more good stuff here

and Here

Nov 27, 2010 | Whirlpool Refrigerators

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what initiates the defrost?

Hi and welcome to FixYa I am Kelly.

Your defrost cycle is controlled by a mechanical defrost timer similar to a spa timer

Download this manual then see pages 13 and 14 for locating and setting the defrost timer.


There are 3 different types of GDM units. NOTE the one 2 and 3 door timer locations on page 13. There are all in different locations.

Also see page 109.

If you need service or technical help:


Thanks for choosing FixYa.


Sep 26, 2010 | True GDM-23 Refrigerator

1 Answer

freezer working but no cooling in the bottom cabin

There is something blocking the cold air from the freezer from reaching the refrigerator compartment. Since you mentioned frost in the freezer section, I can assume that the defrost circuit has failed. This circuit is made up of a defrost timer/module, heater and thermostat. I can't determine whether you have a defrost timer or module since you did not supply a model number.

What you need to do is to unplug the refrigerator, empty the freezer and remove the panel in the freezer section. This panel will give you access to the evaporator motor/fan, the evaporator coil and the defrost heater. Take a hair dryer and use that to melt the ice. Make sure that you monitor the drip pan regularly as you melt the ice since it will fill up with water and you will need to empty it regularly.

Once you get the coil clear of ice, you should see a heating element, it either lookes like a black wire that is attached to the evaporator coil, or it could look like a glass tube with a filament inside. If you have a meter you can determine whether the heating element is working. If the meter resistance setting show it as open, then you will need to replace the heating element. If the element is good, then you will need to check the defrost timer to see if it is turning the cam to periodically run the defrost mode.

If you do not have the ability to troubleshoot the defrost circuit, then call a service company. You can put the refrigerator back together and it should be able to cool the refrigerator compartment, until the service person and fix the problem.

Hope this helps you.

Jul 23, 2010 | Frigidaire Refrigerators

1 Answer

refrigerator runs, cools (freezer too), then stops cooling for a few days (freezer stays somewhat cool), then starts cooling again. Help...:(

In these new fangled ice boxs is what you call adaptive defrost control. Instead of the old tried and true defrost timer, brainiacs have decided to use artificial intelligence to determine defrost.
The basic pattern of adaptive defrost is:
Hey I ain't making this up. The ADC (adaptive defrost control) Counts the number of times the doors are opened, the total compressor run time, and the length of time the defrost heaters were on during the last defrost. This method supposedly enables the adc to work nice in all kinds of conditions, whether hot and humid or cold and frigid climates. COOLING Mode will remain for an indefinite time or until defrost is determined by the micro-processor. When all systems are go for defrost the adc makes the jump to light speed by going into PRE-CHILL, this brings down the temps in the freezer to off set the defrost operation so that the food temp does not suffer dramatic temp rises. Pretty cool ain't it? If the ice box is in pre chill and the door gets opened then a DEFROST HOLD OFF will jump in and not do a defrost for several hours. If the door is continually opened at the end of 16 hours the adc is gonna defrost that ice box anyway. The defrost period varies but is a maximum time of 45 minutes including when the DWELL kicks in. Dwell is the length of time the ice box stays off AFTER the heater is terminated.
Then The POST DWELL will kick in. The post dwell will fire up the compressor and condenser fan but the inside fans will not run allowing the coils inside to cool down before them fans kick in and she jumps back into Cooling mode. I bet you would like to have a copy of GE's adc repair manual wouldn't you?

Dec 22, 2009 | Kenmore Refrigerators

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