I'm working on a carrier Model # 50Zh-036-301 Serial # 5004G31379
the customer complains that the unit freezes up and does not defrost! Of course whenever I show up it is not Iced up! But anyways, I procede to jump the defrost t-stat out and watch the unit run, and it will not go into defrost. I have the timer set at 30 minutes, I wait, and 50 minutes goes by and nothing, the unit does not even try! I than procede to jump out the speed up terminal's and still nothing. Now the reversing valve is good, the unit will switch over from heating to cooling at the thermostat no problem. I thought my problem was in the board, so I picked up a new board and coil sensor from Carrier, and the unit still won't go into Defrost! What am I missing here? I'm about to push this thing off the roof !