I have a Amana/Goodman heat pump which is freezing up. After watching it for a few defrost cycles, I've noticed it doing a few things that would cause the problem. (1) sometimes the valve doesn't reverse at all when I test for defrost, (2) sometimes the valve reverses, but only after being in defrost mode for about a minute, even though the board is showing 24VAC, and (3) when the valve is working fine, sometimes the fan won't kick back on in normal heat mode after defrost. After the valve issues, I just assumed the solenoid or valve was bad, but considering the fan issue and the valve sometimes working fine, would this point to a bad defrost board or thermostat? By the way, filter is clean, airways are open, coolant is NOT low. I would appreciate any suggestions. Thanks!