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Heating & Air Conditioning

Heat pump defrost-cycles but doesn't actually defrost

10 years ago

So I have a 2-1/2 ton Fridgidaire heat pump that is heavily iced up. I thought, "OK, something is going on with the defrost board", so I went out and jumpered the test pins. It seemed to go into the defrost cycle OK, but after five minutes, there was no water coming out and no noticeable effect on the ice.

Hmm. So I put the unit into cool mode to see what that did. Again, no effect on the ice, and the pressure line coming out of the unit was still kind of warm. So what does this all add up to? It looks to me like the reversing valve is not reversing. I can't think of any other explanation.

As I see it, the possible causes of the valve not reversing could be: (1) some kind of fault on the defrost board, (2) a problem on the electrical side of the valve (fried coil or wiring fault), or (3) the valve is mechanically jammed. I was thinking that tomorrow, I may try swapping the board with its 1-1/2 ton brother sitting next to it, but before I do that major surgery I'd like to do some more exploring. Actually getting at the reversing valve is kind of a pain; I have to take the top off and move the fan out of the way, and then lean into the unit to get at it. I can test and replace the coil if that's the problem. But if the valve is jammed, I'm guessing that fixing it will involve opening the system, which is beyond my capabilities.

Any guesses on what the most likely cause of the reversing valve failing to reverse might be? Or am I totally off base here?

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Comments (10)

SpecialtyAirInc
10 years ago
According to what you explained here, I think that your assumptions are correct. You may also try to replace the board. Before proceed to do anything with the valve. Also, there may be a problem of low voltage or a fault in the board which may be solved by replacing the board.
energy_rater_la
10 years ago
and once you get through with all that...
call a pro.

or cut to the chase, save your time & effort
and get it fixed correctly.
taking parts from one unit to install in
another unit is a haphazard way
of determing if something works or not.
if units have to be re-assembled it will cost
more.

call a pro.

best of luck.
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fa_f3_20
Original Author
10 years ago
I've thrown in the towel. I have confirmed that the board applies 24V to the valve during the defrost cycle. And I've applied 24V to the valve manually and gotten a click and a very audible pressure change. Still, the defrost cycle has no visible effect on the ice buildup. Emergency heat today, pro tomorrow.
weedmeister
10 years ago
btw: a large amount of ice is not going to disappear instantly. It will take a while, several minutes.
ionized_gw
10 years ago
Swapping parts can cause unintentional, additional failures. A short in one part might take out another. By swapping untested, defective parts, you might blow out something that you need to run your second unit.

Don't reversal valves need refrigerant pressure to work properly? If you reverse them without the compressor running, will they switch?
energy_rater_la
10 years ago
hope you'll come back with details of
what the pro found out.

and that it is an affordable fix.

best of luck.
fa_f3_20
Original Author
10 years ago
Thanks, everyone. Pro was here today and he wants to replace the outdoor coil temperature sensor. He thinks it is cutting off the cycle too soon. He also wanted to replace the board but I said no to that -- it seems to me that the board is working the way it is supposed to. While he was there I asked him to check the pressures just to humor me. He did and said, "Oh, it's low". He didn't have the sensor in stock, so he's coming back tomorrow to replace that and top up the system.
tigerdunes
10 years ago
Topping off a system usually indicates a leak.

Gas n go not acceptable.

Just so you know.

IMO
fa_f3_20
Original Author
10 years ago
I'm aware that the system has a small leak. It needs to be topped off about every 2-3 years. In the past the indoor and outdoor units have been check extensively with a sniffer, and no leak has ever been found. Apparently it's in the lines between the indoor and outdoor units, and I don't feel like ripping out all of the walls trying to find it.
fa_f3_20
Original Author
10 years ago
So to follow up: The refrigerant wasn't a little bit low. It was a whole lot low -- 7 lbs. of R22 low. Cost me a pretty penny. It has not leaked like this before, so evidently something has happened,. I've noticed that I now hear a gurgling noise in the indoor coil when the unit runs. But for the moment, it's working. So the plan now is to live with it until it leaks down again, and then replace. Don't know how long this will be -- I'll get it checked again in the spring.

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