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Neither Heat OR A/C

 
Old 12-17-2018, 06:33 PM
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Booker42
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Default Neither Heat OR A/C

Hello all - My new to me '87 S4 Manual has developed a problem. I get 'room temperature' air at all settings. The A/C and heat worked when I bought the car a few months ago. I thought it might be a problem with the A/C controller so I found a spare and replaced the original. No dice. I've searched the forums and wasn't able to find anything specific to this problem. I believe the A/C is fine. Any suggestions would be much appreciated!

Brett
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Old 12-17-2018, 07:07 PM
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Mark Anderson
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Check to see if the heater valve is closing when you have the AC on. If it does not close it will never get cold. Lots of AC tips can be found here http://www.928intl.com/repair.htm
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Old 12-21-2018, 02:50 PM
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Old 12-21-2018, 03:04 PM
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A lot of parts need to be working for the whole system to operate correctly.

I would start by diagnosing the health of the various vacuum actuators and vacuum switching solenoids. Easiest to check them all at the vacuum manifold, which lives at rear of radio/head unit if you have one installed (attached to bracket with three self-tappers). With the manifold removed and a Mity-Vac, you can disconnect each vacuum line in turn, and check the actuator it drives to see if it holds vacuum. You also have access to each solenoid (attached to manifold with single screw) to test those, but they fail much less frequently than the actual vacuum actuators.

Before delving into centre console you can quickly check performance by attaching MityVac to the line to the manifold normally fed by vacuum from brake servo (usually attached to 4-way spider that lives under air box). Pump up vacuum, then see if it holds when you turn on ignition.
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Old 12-21-2018, 03:26 PM
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Thank you. I was hoping someone would say that I just needed to clean the controller contacts with Deoxit (which I plan on doing tomorrow). Oh boy, here we go!
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Old 12-21-2018, 06:47 PM
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Originally Posted by Booker42 View Post
Thank you. I was hoping someone would say that I just needed to clean the controller contacts with Deoxit (which I plan on doing tomorrow). Oh boy, here we go!
Unfortunately the controller itself is rarely cause of HVAC problems, apart from obvious faults like one of the two edge connectors not being properly plugged in, or the AC clutch relay failing, or maybe a micro switch failing.

But when you get to do the electrical part part of the testing, you do need to check that the slider varies resistance correctly over full range. Iĺd put money that the problem lies elsewhere at this stage though.
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