Check for vacuum leaks in the circuit that involves the recirc door, defrost and center vent. The center vent defaults closed and the defrost open with lack of vacuum.

As to the heater look at the electrical control of the water valve. I might worry about someone plugging the lines or wiring the thing on constantly. The heat is off with the valve turned on, it also defaults to hot, which is the normal fault and is often bypassed one way or other to get AC.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician