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Old 03-13-2019, 10:09 PM   #1
hessam69
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Default Heater vent control not working

Hello,

On my 1994 940, the vent control knob does nothing. The air only comes out of the windscreen vents regardless of the vent control position.

I'm not sure how to diagnose the problem.

Thank you
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Old 03-14-2019, 01:03 PM   #2
Fa182
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What kind of heater controls do you have? Manual? ECC?

I had a similar issue with my door vents not blowing and found that the cables that control the flappers in the diverter box were all loose. Fixed them back to the diverter box with the clips and some zipties and they are working again.

I do have manual controls without AC though which is cable controlled, the ECC is controlled via vacuum I believe. Depends what you have.
The diverter box is behind the middle of the dash in front of the heater matrix and you can access it enough by taking off the knee panel (LHD in my case).

Here's my thread, maybe it helps: http://forums.turbobricks.com/showthread.php?t=339144
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Old 03-14-2019, 04:11 PM   #3
hessam69
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Hi, I have the non climate control system. The non electronically controlled one
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Old 03-15-2019, 03:21 AM   #4
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So this one?:


I have the exact same unit and it is cable controlled. Take the knee panel off like I said and have a look what the cable does when you turn the knob.
If it is not fixed with the clip to the diverter box, the cable just flexes and does not have enough strength to push the flappers into the other positions.

I don't have a picture of this but you can easily see what happens when you have a look.

Might be some other issue, but this would be the easiest and first step.
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Old 03-15-2019, 06:47 AM   #5
hessam69
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I thought my system was vacuum operated, not sure though. In your case, what caused the cable to become detached?
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Old 03-15-2019, 08:45 AM   #6
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Just have a look, it's easy to spot how it's controlled in your case.

The plastic clip that is holding the cable to the box broke. I just fixed it with a zip-tie. Can't find a pic sorry.
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Old 03-15-2019, 09:41 PM   #7
hessam69
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I had the vacuum check valve installed backwards. this wouldn't be my first time.

So it works now, but I can hear a little hissing and in low vacuum situations the vents stop blowing. Is there a way to find the leak (with a smoke tester or something) Or do I have to pull out the entire dash and go through each and every hose? When putting a vacuum pump on the hose going to inside the car it wouldn't hold vacuum.
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Old 03-16-2019, 03:05 AM   #8
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Whoops! Sorry, can't help with the vacuum controlled system, no idea how it works. Need some other guys to chime in here.
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