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Old 07-29-2008, 07:22 PM
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Join Date: Jul 2008
Posts: 1,236
Unhappy Weird Air Vent Problem

Okay, this is a strange one. I am thinking vacuum leak somewhere.

'90 300SE. A/C runs decent, having been retrofitted to 134A.

With the A/C on, the airflow will come out of the center vents for a little while (usually). Then, without me doing anything to the controls, it will route all the air through the defrost slots.

If I put the system on EC (economy, AC compressor off), the air will come out through the center again. If I switch it back to A/C, sometimes the air will continue to come through the center vents, sometimes it will switch immediately to defrost vents. Sometimes it will run on center vents for a good long while and then just spontaneously switch to defroster again.

One thing that seems to be a pattern is that it will often switch to defroster under acceleration. This is why me thinks this is a vacuum issue.

Question is: Where do I look? What innumerable assemblies have to be removed to get to it?

Thanks much!!

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Old 07-30-2008, 01:01 AM
compress ignite's Avatar
Drone aspiring to Serfdom
Join Date: Feb 2004
Location: 32(degrees) North by 81(degrees) West
Posts: 5,554
Vacuum pod test block

# 59 is the vacuum pod test block (You can plug in your mighty vac to each
pod's circuit and test for leaks) I think you have to pull out the glove box
liner to access it.Be careful with the glove box light!
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Weird Air Vent Problem-screenhunter_09-jul.-29-23.35.gif  
'84 300SD sold
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Old 07-30-2008, 11:05 AM
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Join Date: Jul 2008
Posts: 1,236
I was afraid it meant diggin in the dash. Thanks for posting the diagram. I will try to to a leakdown test on it tonight.

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