Hvac problems

[pauliescff]

1994 525. Every once in a while, the footwell vents will blow hot air regardless of the temperature setting. If I shut the footwell vents off, cold air from the face vents and top vent get warm. this is an intermittent problem that I can't track down. Anyone have any ideas? I've already replaced a faulty water valve due to disintegrated rubber diaphragm.

[GregT53]

Is the ac/recirculate/rear defrost switch functioning normally?

[pauliescff]

Is the ac/recirculate/rear defrost switch functioning normally?

They do.

[GregT53]

GE Does moving the temperature wheel in the center of the two middle dash vents change the air temperature from those vents?

Assuming your system has a full charge of freon and your compressor belt is properly adjusted it may be broken stepper motors. Lots of cars suffer from steppers that break with age because of brittle plastic components. There are also cables that control air distribution. These are attached to the three levers you see on the front panel of the control panel.

To check the cables remove the radio and reach down to the control panel so you can push it out on the steering wheel side. You can check if the cables are fully connected and working.

To check stepper motors you have to remove the glove box to then remove the carpeted trim cover. This gives you access to the steppers. There are several of these. Do a google search for E34 steppers to see images of what you are looking for.

The Bentley Manual gives some information on this at pages 640-4 and 640-5, but it's not very detailed.

If you remove the carpeted access panel take the opportunity to replace the cabin air filter, probably the most overlooked filter on E34s.

[pauliescff]

Everything is charged and functions as intended. I'm thinking perhaps the blend door stepper is acting up? Does anyone know which stepper is the blend door?

[GregT53]

Bentley states there are ten or so steppers so you may be looking at testing more than one.

Have you considered if your IHKR module is faulty? When these go bad unusual problems result. I had a faulty IHKR a few years back and symptoms included a compressor that would not activate, a control panel switch that would not activate the rear defroster, and loss of control with the center temperature wheel. Perhaps someone here knows how to test the module. I diagnosed mine by swapping an IHKR from an E34 with a normally functioning HVAC.