Diagram of HVAC Venting?

Wed Apr 17 13:58:01 EDT 2002

Is there only supposed to be a black plastic cover over the evaporator (looks like it directs the drips to an opening in the firewall and has air vents on it)? That's all that's separating mine from the cabin. When I stick my head under there and hit the AC switch I can hear something opening/closing and hear a difference in airflow (doesn't seem to make a volume difference at the vents). So, I guess it is working properly. I couldn't see anything move, should I be able to?

So, assuming that the venting system is working as designed, how do I check the duty cycle of the compressor? How long/often should it be on? How do I check whether the temperature control needs adjustment? How is it adjusted? Sorry for all the dumb questions, but I'm not a good mechanic...

Dave

1987.5 Audi Coupe GT "Special Build" 2.3 - Anthracite Black
1998 VW Passat GLS 1.8T - For Sale CHEAP

-----Original Message-----
From: Ti Kan [mailto:ti at amb.org]
Sent: Wednesday, April 17, 2002 12:26 PM
To: David Ullrich - 0018 HQ
Cc: ti at amb.org; quattro at audifans.com
Subject: Re: Diagram of HVAC Venting?

Ti Kan wrote:
> With the hood up and the plenum cover off (that black plastic rain drip
> thing that also covers the wiper motors), you should be able to see the
> vacuum solenoid operate when you move the temperature lever to full
> cold and turn on the A/C.

David.Ullrich at ferguson.com writes:
> OK, the "evaporator" (I can never keep straight the evaporator and =
> condensor)is getting plenty cold. That little vacuum solenoid DOES move =
> when the AC switch is flipped on. But I don't hear any change in air =
> flow nor does it seem to change the air flow pattern/amount. Any =
> suggestions on what to look at next?

If you look into that air box from the passenger side opening you should
actually see the air flap move.  If that's moving ok then it should be safe
to assume that all is well there.  I don't think you'd be able to hear/feel
any change in air flow pattern or amount within the cabin by that alone.
On these cars, the air flow pattern is manually regulated by the two
levers at the control panel, and the flow amount is governed by the
blower fan speed.

Since A/C cooling is controlled by cycling the compressor on and off on
these cars (rather than mixing ambient v. cooled air like on other
more modern Audis), you might want to pay attention to see if your
A/C compressor clutch is cycling, and if so, what is the duty cycle
(how much time on and how much time off).  If the compressor is not
running much then maybe the temperature control needs adjustment.
Note, though, that there is also a capillary tube that runs from the
temperature control to the evaporator, that overrides and turns off the
compressor to prevent the evaporator from icing up.

-Ti
01 S4 2.7 biturbo quattro
84 5000S 2.1 turbo
80 4000 2.0
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    ///  Ti Kan                Vorsprung durch Technik
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