Cold Air From the Center Vents

Document history:
# 20 Jan 2003: Updated the part number information.
# 24 March 2003: Rewrote the entire procedure.

Problem: Only cold air comes from the center vents. There have been discusions on various message boards that this is supposed to be normal. Granted it's not supposed to blow out hot air, like the demister and footwell vents, but the air should be warm as the image bellow indicates:

When this happens it's most likly that there is a broken steppermotor mount on the heater housing. The steppermotors held by these mounts control the mixture of hot and cold air that comes through the center vents.

Background: There are 3 different heating systems used in the E32. One from Siemens, a heater unit from Behr and the climate control from Behr.

The proper way to fix a broken stepper motor mount is to replace the center housing of the heater unit. But since this requires taking the entire heater housing out of the car various "quick fixes" have been applied with success.

Models: All E32s and E34s with a Behr heating or climate control system.

Quick Fix: To get to the motors you have to at least remove the radio. Removing the center console also helps getting better clearance to work.

I tiewraped the motor to anything within reach. This includes the metal support frame and the brackets on the heater housing that are used to attach the heater wiring.

In my case this solved the problem for a short time. After owning the car for about a year the center vents decided to blow only cold air. After checking the steppermotor mounts and found that they where all in working order I removed the entire dash decided to find the problem.

What happend in my case was that on the pasenger side the plastic lever that controls the mixing flap had worked loose. This lever can be seen through the footwell airduct. To access the footwell flap remove the stepper motor for the flap. This allows you to open the flap by hand. After pushing the lever back the passenger center vent blow warm air again.

After removing the upper dashboard cover I found these pieces of plastic in the hinge area of the driverside mixingflap. As it turns out the mixing flap was broken. This may have happend at the last aircon refill when they inserted a temperature probe into the vents.

This is the mixing flap and the control lever. The flap is suppost to have a square hole where the lever fits into. But as you can see it's broken.

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If you would like to add any comments, remarks and/or corrections to this procedure, feel free to email Mike Oswald and we'll put it on our site. Share your experiences with us so others may benefit from it.