[s-cars] Windshield fogs up in cold weather & AC is off

[chris chambers]

As I understand it, there is a sensor that turns the compressor off when the pressure is too low or too high pressure. 

I think you could test by locating and bypassing the compressor's relay, it's located in the relay box in the engine bay.

If the compressor turns on when bypassing the relay, I would suspect either a failing relay or an issue with pressure.
If you have ready access to a relay i and would try replacing the relay, otherwise I would have the system's pressure checked by a tech.  


HTH
Chris





>________________________________
> From: Thomas Rodriguez <trodri69 at gmail.com>
>To: Joshua van Tol <jvantol at gmail.com> 
>Cc: s-car-list <s-car-list at audifans.com> 
>Sent: Sunday, November 18, 2012 8:57 PM
>Subject: Re: [s-cars] Windshield fogs up in cold weather & AC is off
> 
>Thanks for the tips.  Here are a few more observations.
>
>Tonight it was about 42F outside and this temp was accurately
>displayed on the instrument panel readout.  I had the heater set to
>70, the AC compressor was running fine and all the windows were clear.
>Then just like that the AC compressor turned off and all the windows
>fogged up within a couple of minutes.  Pressing the AC button on the
>HVAC control panel would not turn the compressor back on, though the
>AC indicator light would come on as long as the button was pressed.  I
>shut of the heater, zipped up my jacket and opened all the windows to
>clear the fog from the windshield. Ten minutes later I got home and
>turned off the car.  Five minutes after that I started the car and
>turned on the heater, and the AC compressor was working fine.  For
>kicks I manually turned off the AC compressor with the button on the
>HVAC control panel and the windows fogged up within a few minutes.  I
>manually turned the AC compressor back on and the windows cleared
>right up.
>
>Something is causing the AC compressor to turn off at temperatures
>well above 32F (note this was not a problem in the warm summer
>months).  Is there a sensor or switch that may be going bad?  Perhaps
>it's a problem with the connection to the on/off button on the HVAC
>control panel on the dash; many of the other buttons on this control
>panel (e.g. temp and fan speed) function only intermittently.
>
>If anyone has had these symptoms and found a fix, please let me know.
>
>Thanks,
>Tom
>'95 S6
>
>On 11/18/12, Joshua van Tol <jvantol at gmail.com> wrote:
>> Could be that the recirc flap isn't opening.
>>
>> On Nov 17, 2012, at 11:21 PM, Thomas Rodriguez <trodri69 at gmail.com> wrote:
>>
>>> Now that the weather is cold my windsheild fogs up when I run the
>>> heater or defroster.  I believe this is because the AC is not
>>> operating when the outside air temperature is cold, so it doesn't
>>> remove the moisture from the air before it passes through the heater
>>> core.  It is my understanding that the AC is supposed to run in the
>>> winter expressly for this purpose.  The AC indicator light on the HVAC
>>> control panel is unlit.  If I push the AC button on the control panel
>>> the indicator light illuminates as long as I hold the button down, but
>>> goes out when I release the button.  I am confident the fogging is not
>>> due to a coolant leak into the HVAC system; I recently replaced the
>>> heater core and there is no coolant odor inside the cabin and no drop
>>> of coolant level in the reservoir.  The heater works great (aside from
>>> the moisture) and the AC worked great during the summer.  Am I correct
>>> that the AC should be operating in concert with the heater &
>>> defroster?  Any tips on how to correct this?
>>>
>>> Thanks,
>>> Tom Rodriguez
>>> '95 S6
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>>
>>
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