Does it change at all if you cycle through the heater and AC modes and auto/manual settings?
What about if you go through the entire range of cooling of heat? Would there be any settings that work correctly as expected?
I am almost sure that one of the flaps in the HVAC system is stuck. Not sure if Quest’s system is servo-motor driven, or vacuum driven, but either way, need to go through the modes/ranges and see what does not work, than summarize that and check against the service manual to see where to fix.