Ford Repair: ac climate control, lincoln town car, vacuum controller

Question
1990 lincoln town car. The ac blows cold until engaged in drive, then blows hot like the heater is engaged. I have changed accumalator, 2 hoses, and have had it charged. Tried to find repair manual for inside the dash components. No luck..any suggestions? Thank you

Answer
Sounds like a problem with the blend door which I think is vacuum operated on this vehicle. Do you hear a hissing sound under the dash? The vacuum controller on this vintage would fail and go directly to heat. When yo put the car in drive the engine vacuum changes slightly. Otherwise I can think of no correlation between the two.
This controller is behind the glove box area.