I see this is an old post and you may already have your problem solved, but I had the same problem with my enclosed flybridge A/C. Considering my vintage (1979 60C EFBSF), I probably have a similar A/C system configuration to what you have.
According to the previous owner of my Hat, they thought (or someone advised them) it was the Tstat control. I replaced the entire three knob control with a new one. Same problem continued....Heat only. I checked all the wiring schematics and all checked. Apparently someone has crossed wiring in the past or I have a PC board problem. For the interim, when I realized heat mode of the reversing valve requires the valve to be energized, I unplugged the valve, sealed off the connectors with rubber boots and it has been working fine in cool mode (which is all I use up there 95% of the time anyway) until I get a chance to reevaluate all the wiring. So for now, I have been able to move that item down to item # 365 on my list. I would just make sure to safely and thoroughly protect and cover both ends of the dis-connection.
I am with you (and all others) on the despair with Cruisair. The older units kick butt without any problem. The new, more delicate units (as with MTU engines vs. DD) need more TLC. Definitely not preferable offshore.
This is a company I have been checking into: Flagshipmarine dot com (Check out the high pressure central system. Seems like a very efficient concept). This company seems similar to Cruisair before it was junked out/complicated by Dometic. All off the shelf parts, easily serviceable, high quality construction and affordable, etc. However, I don't have experience with their systems, or know anyone who does. They just seem like someone to check into if you are considering a total system replacement. Maybe others have knowledge of them.
Good luck!
Alan Dubuisson
1979 60C EFBSF