View single post by jackpai
 Posted: Wed Aug 31st, 2005 05:25 pm
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jackpai

 

Joined: Wed Aug 17th, 2005
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shogun wrote: I have the same problem with the defrost cycle and need help diagnosing if it is the control board or the thermostat/element.

Here are the facts:

1)The first time I jumpted L1 and test the defrost cycle went on for about 20 minutes(removed back wall to confirm this).
2)Subsequent tries (while frozen over) stopped the motor but did not turn on the element).
3)There are no burn marks on the board to indicate a burnout.
4)The resistance on the thermostat measured 240k ohms with slight fluctuation +- 20k between hot (room temp.) and cold (15 degrees).
5)The 2 year full waranty just expired (my luck).

Can you tell me definitively samurai if the board or the thermostat is the culprit, or, do you have any further diagnostics to confirm which component is at fault?

To confirm your facts, you did see the heater glowing when you forced the 20-minute defrost cycle and the evaporator was frozen at the time of testing.  Then subsequent tries failed to trun on heater when evaporator was iced over.  Am I correct in interpretating your facts?

The thermostat will close when it's iced over, the heat element will be energized when defrost cycle active.  When ice started melting to a certain point, the thermostat will open to prevent further defrosting regardless the cycle is active or not.

The best way to find out exactly what's wrong is to measure the voltatge between L1 and the DEF HTR when plugged in and in defrost cycle, make sure there's 120V AC.  Be very careful to do this due to risk associated, depends on your electrical skills.   Or you can remove the board, and apply 24V DC (12V should be able to do it too) to the relay coil and measure the continuity between the SPDT's pole and Def Heat (3 leads, one pole, one NC to compressor and one NO to heater).  The relay could click but not make good contacts everytime to energize the heat assembly.

From what you observed, you may have a bad relay or an intermittant teministor.  If you can measure 120V AC or good continuity on relay everytime it clicks, then you have a bad terministor.