AC coming out of passenger side, but hot air on driver's side

[vayu17]

Hey gents,

When I start the car from cold after sitting and turn on the AC I get cold air out of the passenger side vents and Luke warm air out of the driver's side vents. As the car warms up the air coming out of the driver's side vents becomes hot, like the heater is on...passenger side remains cold.

One suggestion was that it is the heater AC water valve. My mechanic seems to believe it is a servo motor or blend door. Any suggestions? I'm at an impass.

thank you

[Timm]

Could be either - but the way you find out is to put the drivers temperature to 16C (fully left past the 'click'). In that position both heater valves should be closed and the pipes running to the heater matrix should be cold when the engine is running. Here's how you get to the heater valves:

http://www.meeknet.co.uk/e31/E31_Hea...eplacement.htm

[taylorpatterson]

Stuck or broken mixer flap on driver's side is my bet. Many folks have been through the same symptoms including myself. Had to remove the dash and get to the IHAK box to repair the broken flap.

[bruinbro]

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[gary8]

You should hope it's the heater valves, otherwise you are in for at least two full days. To diagnose mixing blend door issues before removing the dash, remove the panel and floor vent duct under the steering column to view the floor vent door. With ignition on, use the left controls to open the flap and observe the rod movement within the white plastic bell crank's slot. It may be disconnected or binding because the other end of the rod is out of alignment due to a broken hinge in the blending door above, and/or the top left stepper motor mount has broken off from your IHAK unit. You can remove the center vent and/or MID to reach the top left stepper motor to see if it is loose.

Here's what I think it occurring in our cars at this age. The left and right blending doors open and close with very close tolerance within the rectangular ducts. Over time (about now), they bind. As the stepper motor tries to force open and close the door, it breaks the mount and/or the hinge.

IMPORTANT note for your car. You'll likely want to test the operation after the repair, but if you connect the batteries and turn on the ignition with the air bag in the steering wheel disconnected you'll trigger the SRS light. The SRS light in cars older than 1994 cannot be reset using INPA/DIS/Autologic/ Snap-on/Peake tools because they cannot communicate with the older SRS module. We didn't know that and are still are trying to get bruinbro's light off and have tried http://www.bimmerforums.com/forum/sh...-Special-Tools

Good luck!

[bruinbro]

And replace the heater core if you end up removing the dash.

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[vayu17]

Hi Timm,

I know you commented on this last time I posted. So if I put the driver's temp to 16C, and still am getting warm air...then it is NOT the heater valve? Could you clarify for me the test, please? Thanks again.

- - - Updated - - -

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That looks like a whole lot of fun.

[Timm]

If you put the heat on the drivers side to 16C and things still get hot - it IS the heater valves. Both valves should be closed at 16C.

[bruinbro]

That looks like a whole lot of fun.

All 3 days of it. And 3 people, one of which knew what he was doing (not me).

[bmw528e11]

And replace the heater core if you end up removing the dash.

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+1 had my dash out a year ago.. But didn't know that heater core can leak... What you know, it's sipping.. Can smell a strong coolant smell as I turn the a/c or heater ON.. Scarry and unpleasant feeling while driving..

[Shockleysprings]

My solution after replacing the heater valve w/ no luck, was to install a manual valve where the hot water goes from the heater core to the heater valve. In the summer it stays closed and I've got great AC. In the winter I open the valve for heat. I will repair the flaps when I do the heater core at some point in the future.

[noelher]

Hi Shockleysprings,

Your post was great, I am thinking of the same temporary solution but want to get some confidence from members whose done it. Did you cut the feeder hose to the heater valve and install a manual shut off valve? What is your opinion of a pinch-shut with a clamp? which is a very quick temporary fix.