a general defrost question

[cuzzin sam]

I unfortunately don't have the model # for this GE side by side but I'm hoping someone can shed a little light anyway.

I first went to this call and found the evap frozen and the defrost heater burned out. I replaced the hearer, defrosted and left only to be called back a few days to find the evap frozen again. The heater and the termination thermostat both read closed so as an experiment I jumped around the thermostat, defrosted and left.

A couple of days later it was frozen again so thru a process of elimination I decided it had to be the board...which I changed...and of course it's frozen again. This parts changing idjiit is getting tired.

Does the board send the unit into defrost based on time or is there a thermister or something that tells the board when to initiate a defrost cycle? If I jump the terminals on the board (I read that here last night) am I simply supplying voltage to the defrost circuit or am I closing the defrost relay on the board? And the big question, has anyone ever seen someone change so many parts with no appearent idea of what he's dong? Thanks for the desperately needed help, Sam

[RegUS_PatOff]

... or is there a thermistor or something that tells the board when to initiate a defrost cycle?

yes ,. when to terminate the Defrost
The Control Boards usually have a test for ther Thermistors and the Defrost Cycle
Freezer may have (2) of these
Fridge may have (3)
click on picture


the "older" style were prone for failure
http://fixitnow.com/wp/2010/06/30/ge-profile-and-arctica-refrigerators-upgraded-thermistors/

[Samurai Appliance Repair Man]

No, the board decides when to initiate defrost based on door openings, and other factors. The evaporator thermistor tells the board when to terminate the defrost; the board terminates defrost when the thermistor reads 75F. Now, suppose the thermistor's resistance was such that the board always thought it was 75F, what would happen? Answer: the board would never initiate defrost because it thought the evaporator was already too warm.

Check the thermistor resistance by placing it in a glass of ice maker. Should get about 16 K-ohms. If it's one of the old style, it needs to be replaced in any event.

Thermistor part link ==> http://www.repairclinic.com/PartDetail/Thermistor/WR55X10025/914093