Thanks for your response. I did check the defrost thermostat and I do have continuity. I would be interested in knowing how to force this unit into a defrost cycle. What do you think about the thermisters being bad would that keep the unit running all the time?
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Re: GE refrigerator not defrosting
To force this unit into a defrost mode, unplug the fridge and remove
the cover from the main control broad and remove the main wire harness.
(Three wires, Black, Blue and Brown I believe) Next take a a small 3in
wire and bend it into a U shape to make a jumper.
Insert the jumper into the main wire harness to jump the to outer wires
together. (Black to Brown) It should be pretty easy to slip it in
through the back with the rest of the wires. (Don't worry this test
will not cause any harm to your fridge)
Now reapply the power to the fridge and check the defrost heater. As
long as the defrost thermostat is below 15 degrees then the heater
should start working. If the heater doesn't work then there is a
problem with either the defrost thermostat or the heater. GE uses a
glass tube heater with a coiled wire inside. This wire has a habit of
breaking after a few years.
As far as the thermistors go, all the do is tell the board to cool.
They can make the unit cool all the time but the board should still
defrost the evaporator every 6-36 hours. If the unit starts defrosting
then you have a bad board.
Hope this helps and let me know if you need any clarification. Good Luck!
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Ice build-up in the freezer compartment is an indicator that the defrost system is not working properly.
The defrost system is composed of the defrost heater and the defrost thermostat. If one of them is not working, ice will build up in the freezer compartment.
You need to do a continuity test on the defrost heater and if it is good, very likely the culprit is the defrost thermostat. Just replace the thermostat
Refrigerators that self defrost have three main components that cause defrost to take place. On your model GTH18ECC2RBB there is a WR55X10397 Defrost Control Board
This part is most likely the problem and is found inside the fresh food compartment and inside the control panel. The location is 257 in this photo HERE Sometimes the defrost control board will show burn marks but not always. The other two parts that may be defective are the WR51X10038 Defrost Heater
The defrost thermostat is location 630 in photo HERE a tutorial of how to test the defrost heater and defrost thermostat can be found on the parts pages listed above. I will try to put the defrost heater test below. I think the defrost control board is most likely the problem here so look it over first. Manually defrost the evaporator with a hair drier so you can remove the defrost heater and test for continuity. I am here should you have questions Thanks Sea Breeze
Since the heater has continuity it is good and does not need to be replaced, the other parts that can make a ref. not defrost are the defrost thermostat or the defrost control (mother) board.
To check the defrost thermostat it must be checked when cold,when cold it should have continuity on it. The defrost thermostat is in the freezer clipped to the TOP of the evaperator coil usually on the right side...this is what it looks like
If the defrost thermostat has no continuity when cold it is bad and thusly the problem...if it is good and has continuity and already having determined the defrost heater is good..the problem is going to be the motherboard since a part of it is the defrost control.it is the back of the ref.on the left.
you can jumper the board where the line cord enters the board,it will say comp/defrost/neutral in the center,jumper between the center terminal and the outer one that says defrost,if it still doesnt defrost you need to disconnect the defrost heater and check for continuity,then do the same with the defrost thermostat,but the thermostat needs to be below freezing to test it or it will show open(bad) the heater will show some resistance to be good
First, locate the defrost timer which may hidden behindcorners of the fridge at the back bottom, in some models located in the ceilingof the fresh food section or behind the cold control cover. Once you locate thedefrost timer, slowly turn the screw in the middle of the defrost timer withstraight screwdriver until the fridge shuts off. Now it's in defrost. If thedefrost heater(s) starts, replace the defrost timer and defrost thermostat. Ifthe heater(s) does not start, unplug wire cord to check ohm test for continuityof heater. If continuity is there, plug cord wire which gives power 120volts(check specification) to heater. If heater no starts, bypass defrost thermostatby join the 2 wires in the defrost thermostat. If the heater now comes on,replace the defrost timer and defrost thermostat. If the heater itself is bad,replace it. Thanks and hope helpful.
1. Check defrost timer. 2. Check defrost thermostat. 3. Check defrost heater. One of this are more than one may be defective replace. First, locate the defrost timer which may hiddenbehind corners of the fridge at the back bottom, in some models located in theceiling of the fresh food section or behind the cold control cover. Once youlocate the defrost timer, slowly turn the screw in the middle of the defrosttimer with straight screwdriver until the fridge shuts off. Now it's indefrost. If the defrost heater(s) starts, replace the defrost timer and defrostthermostat. If the heater(s) does not start, unplug wire cord to check ohm testfor continuity of heater. If continuity is there, plug cord wire which givespower 120volts (check specification) to heater. If heater no starts, bypassdefrost thermostat by join the 2 wires in the defrost thermostat. If the heaternow comes on, replace the defrost timer and defrost thermostat. If the heateritself is bad, replace it. Thanks and hope helpful
The next step would be to unplug the refrigerator and remove the rear panel and defrost so that you can unplug the defrost heater on one end and check the continuity. 305175 Defrost Heater and defrost thermostat Part number 3489. If you change the defrost heater you should also change the defrost thermostat. Let me know the results. Remember above 60 degrees the defrost thermostat will show open with your OHM meter. Sea Breeze
The timer is controlled inside the control board on rear of your refrigerator. Four possibilities are the defrost element, defrost thermostat, Temperature CLIP EVAP THERMISTOR or the control board is defective. Let me know if you would like me to help you on this, Thanks, Sea Breeze
CHECK THE DEFROST HEATER FOR CONTINUITY. IF IT IS O.K. CHECK THE ELECTRONIC CONTROL FOR A FAULTY SOLDER CONNECTION ON THE DEFROST RELAY. THE ELECTRONIC BOARD SHOULD BE LOCATED ON THE BACK WALL OF THE REFIGERATOR BEHIND AN ACCESS PANEL.