THE heater in my 85 760 turbo does not work in temps. under 30 degrees. It has auto climate control. When it is turned on,it pulls in outside air to freeze you to death. Does this have a relay to replace on the temp. control unit or is a door stuck on the plenum? I have tried the water control valve on the hose to the heater in the engine compartment and it is o.k. ? Any ideas? " Boss 302 "

 

Maybe one of the Vaccum soleniods.

 

I'll try the solenoids when I get to them, it looks like quite a bit of work. thanks Boss 302

 

Also make sure the thermostat is good.