I have an American Standard Heritage 11 system that is just over five years old. The coils freeze up when I have the heat on. After some research I assumed that it was the defrost board and had a technician out who verified that the defrost board is the problem after ruling out other possibilities. The light on the defrost board is not on and he is not able to jump start it. I am told by other HVAC contractors that the sensor typically needs to be changed out if the defrost board is changed. My technician does not know what the sensor I am referring to when I tell him this. He is coming to install the new board tomorrow and I'm afraid that if the sensor is also bad, it could damage the new board. Also, how could he test to see if it's maybe a problem with the reversing valve? He said that all of the lines are flowing. The psi test on the high side is 150+ and low 50+; amp test on compressor was 11-15 amp.
Can anyone offer any insight? I would greatly appreciate it.