If you don't get an answer and you can see/touch the inlet and outlet hoses. Start the engine in the coach. and place your hands on the hoses. The heater core inlet side will feel much hotter than the outlet side. If you have an infrared laser thermometer point it at the hoses, the inlet will always be hotter than the outlet.
[SIGPIC][/SIGPIC]2016 Newmar Dutch Star 4369
Newmar Owners Club
USAF 1966-1969,- Law Enforcement 1969 - 2003, Retired since March 2003