Vehicle is stuck in cold mode. Compressor stays on and cant get heat. I have already tried replacing the compressor, the servos are all good, all wiring and hose in right place. I have been at this for three days trying to figure it out with a similar car with working heat side by side as a reference.

Please any advice would be appreciated.

Does the heater valve open to allow hot coolant into the heater core?

When selecting full heat on the temp control knob does the system respond by sending air to the footwell vents? If so, the system at least understands and is trying to comply with the request for hot air....which is a good start

Cheers
DD

By the way it's normal for the compressor to stay engaged. All air is cooled first and then heated as needed

Cheers
DD

Does the servo motor change positions when you move the temp setting? If not then check that the resistance varies across the blue and white wires on the temperature dial(variable resister). Then check the reistance on the cabin air temp sensor which is in the dash. Then then resistance on ambient sensor which is on the side of one of the blower motors. If all three sensors check out then your amplifier is probably bad.

Icsamerica, your suggestions apply to the Delanair MkII system. Since this is an '89 Ser III it'll have the later Delanair MkIII system which is a different animal.

Not trying to bust your chops. I just don't want anyone looking for things that won't be there :-)


Cheers
DD