Nordyne heatpump defrost problem

[thomasd]

Hi,
I was wondering if someone here might be able to give me some repair information for my mom's Nordyne heat pump. Last summer it was blowing fuses in the air handler inside. I tracked the short down to the defrost board in the compressor unit. I replaced it and all was well during the cooling season. Now the outside unit keeps freezing up and it doesn't seem to be entering the defrost cycle. I did the test that came with the new board and it will enter the test defrost cycle and work fine. One part of the test jumpers the defrost t-stat and the cycle starts. This was two weeks ago.
My question is if the board checks out what are the other possible problems.
Is the defrost t-stat bad?
What actually triggers the defrost cycle in the logic board? Is it the number of compressor hours?
I live out of town and my brother called me this afternoon my brother called and said that the coil was frozen up worse than ever.
Any ideas?
Thanks in advance

[thomasd]

Sorry that I don't have the model number right now. I am 80 miles away from the heat pump. I am going to try to go down today and check on things and get the model number I know that the defrost board model number is 624626.Any help would be appreciated.

[gordo48111]

Check this link for basic explanation of a heat pump cycle. It may or may not be of help to you.

http://www.achrnews.com/Articles/Servic ... 00f932a8c0____

[Robert]

Every time I replace a defrost board, I replace the defrost t-stat as well. That could be the problem among other causes.

With it being a heat pump, I would call an hvac tech out to at least get a proper diagnosis.


Thanks,
Robert