Vacuum

No, it's not vacuum. The temperature is controlled by the use of an air mix door that is operated by an electric motor/actuator. This door can be jammed or the actuator can be inoperative or have stripped plastic gears internally.

The actuator is the motor that operates the door. It is powered by the main A/C controls.

It's mounted on the lower side of the HVAC housing which is very difficult to access.

Description and Operation

The A/C electric blend door actuator is located on the plenum assembly.

* Its function is to move the air temperature blend door on command from the control assembly.
* The A/C electric blend door actuator contains a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the air temperature blend door.
* A 5 volt signal is applied to the ends of the potentiometer. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the Electronic Automatic Temperature Control (EATC ) module and is compared to the desired wiper voltage determined by the EATC module. The control module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the desired wiper voltage.

Sure, it's possible to remove the motor and position the door manually but that would be pretty foolish and impractical. The issue here is getting access to it. The part is only about $100 if the actuator itself is bad. It's what it takes to get to it. It's in the general area of ahead of the console.

I'm afraid this is the end of the line for me. You need an electrical technician to troubleshoot the problem on site.