Pente, our 2000 Catalina 36 as factory installed air conditioner. Based on the tag (see picture) has reverse heat feature.  Could somebody please compare the tag on your boat with the attached and confirm yours is same.   My wife and I have both attempted to change the settings to get reverse heat but no luck.  We have followed the manufacturers detailed manual and no heat.   Not to worry, I brought plug in electric space heater and extra sleeping bag.  Your suggestions would be appreciated.