A related problem that I have is the heater box does nothing but heat. I have the Climate Control System in a '96, and recently all it can do is put out heat, unless the max AC is on. Then it seems to get cold, but I think its just the AC is overpowering the ongoing heat.
The air flow directional controls work ok (vent, floor, defrost, etc.), and, when the "automatic" is selected the fan responds properly, varying its speed relative to the difference between desired temperature and the actual inside temp.
Engine temp is running lower than normal, coolant level is ok. I guess its just the heater core functioning as an additional radiator?
Any ideas as to what's up with this? Thermostat? Heater core valve switch stuck open? Is it a pneumatic switch? Or, maybe some valve or switch within the dreaded climate control system itself, buried deep within the dash. (Dealer wants $1K to get into that box.)
Its not too bad a problem right now with the cold weather, but I gotta get this fixed, cause I want to keep the car.
Larry El Cerrito, CA