1984 Carver AC. Salon AC is a Marine Systems Air Model CM16H
Symptom: When started on heat cycle, the unit will operate for 3 to 5 minutes. Then the compressor will shut off. About 30 seconds later, there will be an extreme spike in amperage draw and the main 100 Amp AC breaker will trip. The water pump breaker does not trip nor does the salon AC breaker. Just the main 100 Amp breaker

The Fwd and after AC units operate with no issues - its just the salon unit.

Yes, I have strong water flow out all 3 of the outflows (2 on port, one on starboard). I have opened and cleaned the pump strainer several times.

I have removed the return air vent and cleaned the filter. I tried testing by run the AC unit on heat mode with the return air cover removed and it did not change anything

When the compressor shuts down, it is not warm to the touch (I thought it might be overheating)

My marina mechanic spent a very short time troubleshooting (its haulout time where I live and he is very busy). He told me that he tested the Freon and said it was fine.

If I run the system on Cooling - I have no issues at all. Its only on the heat mode.

My marina mechanic suspects that it is the reversing valve. I had no idea what that was - so I did a bit of Google research. It seems to me that if the reversing valve were sticking - I would get no heat at all. That is not the case. When I run it on heat mode, I get heated air blowing into the salon. It runs that way for about 5 minutes and then the compressor shuts off. The air handler/blower fan continues to operate and move air. About 30 seconds later, there is a spike in amperage draw and the main 100 amp breaker trips.

I shut off the salon ac unit, reset the 100 amp breaker, and i can turn the ac unit right back on in heat mode.

Any help would be appreciated