Heat Pumps and Electric Heating - York Heat Pump Icing. Is the defrost board broken?

Hello,

Recently this past month my York Heat Pump has been icing up a couple times (see picture on link below). I've had to hose out the ice a few times - otherwise HP runs and puts out good heat today. After further research, I've narrowed it down to a broken defrost board. So handy with my tools, I took apart the heat pump today to take a look at things. What do you know, I see a burnt resistor on the deforst board (# 031-00251C) - with open circuit on resistor (infinite). Please see lots of pictures here:

Picasa Web Albums - miki - York Heat Pum... (http://picasaweb.google.com/mdn425/YorkHeatPumpDefrostBoardLogicModuelDefectiveJustNeedYourExpertVerification?authkey=4R4cX-EJ8IM#)

I am fairly certain that if I replace this deforst board, the unit will not ice up again, but wanted to check on this with you first. Is there something else that I am missing, or should be checking as well? :confused:

I could not locate the York model number, but suspect it to be made in the mid '80's (the age of my house). House is 2700 sq-ft. When I turn the Heat Pump off outside, the unit inside runs on emergency heat as designed - so we still have heat.:o

Thanks in advance,
Miki
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Picasa Web Albums - miki - York Heat Pum... (http://picasaweb.google.com/mdn425/YorkHeatPumpDefrostBoardLogicModuelDefectiveJustNeedYourExpertVerification?authkey=4R4cX-EJ8IM#)

High kudos on one heck of a job diagnosing the problem. I think you are on the right track, but just to be sure you've not overlooked some other things here's a few other ideas.

Check any sensors you might have to at least partly eliminate them. On the charge front, make sure the system heats fine. You can check your indoor delta t temp near closest register and at your filter. Don't remember exactly what that should be so start another post on the delta t. You can also check your defrost by putting a little snow (looks like you have some just lying around doing nothing) on the outdoor cool, kick your system into cooling mode and see if it melts withing 10-15 minutes.

I'd say if all this checks out, spring for a new board.

I'd go with a new board. Unless you are really good with working on board putting in a new part on it itself.

Thank you both. I will go ahead and buy a defrost board tomorrow and cross my fingers. I will follow-up soon afterwards.

-Miki

Success!

After getting my new board, I had to also clean off a couple of my sensors. I had to clean off the coil (discharge) sensor - basically use wire brush to clean contact points on sensor and copper line. Perhaps this might help some readers out there on trying cheap (free) methods first.

I had also bought a new sensor just to be safe, but found that the "recommended" sensor behaved opposite of the current sensor. Meaning that the current sensor would open circuit when cold and close circuit when hot. I read everywhere that the sensor should close with cold to put heatpump into defrost mode and then open up at say 60degrees when coil is warm to get out of defrost mode. Again, my sensor behaves the other way around; as I took out my old sensor to test in house in hot water (close) and in ice water (open).

Any hoo.. it is running fine now and defrosting as it should.