Heat pump defrost-cycles but doesn't actually defrost
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?