Z31 Getting Hot Air From AC even when set to cold temps

Hot Air From A/C Vents

Commonly, air flow or temperature control issues are vacuum-related without a single universal cause or fix.

• Any leak in the vacuum system can cause not only heating and air conditioning issues, but also engine performance problems.
• Check the two vacuum lines at the firewall on the passenger side for cracks and leaks. One line goes through the firewall to supply vacuum to the climate control solenoid array, while the other controls the water cock.

There are also three vacuum lines that run back along the fender well to the vacuum canister . Inspect all of these lines for cracks and leaks. Replace any that feel hard or brittle. Most lines are color coded: at the canister there is a blue, a white, and a red striped line. Once identified, run new lines and remove the old ones.

• White: Connects the manifold vacuum source to port M on the vacuum tank (should have a built-in one-way valve).
• Blue: Runs between the water cock and the magnet valve on the vacuum tank.
• Red: Goes between the interior door controls and a live feed from the tank, sometimes labeled as "F".

Click image for larger diagram.

Defrost Vents are the only ones getting any air and it is hot

This issue is becoming more common as these cars age past 40 years. The main causes are vacuum lines running to the actuators that have perished or cracked, or failure of the actuators themselves. The most common actuators to fail are the blend door actuator and the defrost actuator.

Unfortunately, these are also the most difficult to access, as they're mounted on the back of the heater box, buried deep in the dash. This means the entire dash and heater core need to be removed for replacement. From experience, the smaller actuator on the back (blend door actuator) is especially hard to source.

However, you can use aftermarket actuators as replacements with the help of 3D printing for brackets or adapters. Thanks to Nick Sturgis for developing a process that makes this possible.

Intake Actuator

Actuator: Dorman 604-934
3D Printed Mount: Dorman 604-934 Actuator Mount

This is the easiest to use and mount—no need to modify the linkage. Simply remove the e-clip from the original actuator and swap it over. The Dorman 604-934 is a 2-stage actuator just like the original. The angle of the door may differ slightly but it should function properly.

Power Servo 1

Actuator: Dorman 604-922
3D Printed Mount: Dorman 604-922 Actuator Mount

For installation, saw off the last 2 inches of the actuator, then put a right angle in the bracket and use the existing hole to butt against the hardware. Use the actuator's mounting slots to attach the 3D printed mount.

Power Servo 2

Actuator: Dorman 604-933
3D Printed Mount: Dorman 604-933 Actuator Mount

For this actuator, trim off the plastic mounting features and saw off the end of the linkage. The Dorman 604-933 has more travel than the OEM actuator, so the first half-inch of travel does nothing; the next inch actuates the assembly. Refer to the images below for modifications and mounting.