RE: A/C recirculation/warm air from dash ponderings..

["R. Cummings" <cumm@flash.net>]

The hissing you hear when you turn the system off is the refrigerant
equalizing and not condensate being cooked off the system. Shutting off the
A/C at the same time as the engine, does cause the low side components to
frost. On the contrary, the refrigerant on the high pressure side bleeds
through the expansion device to the low pressure side and so the pressure in
the evaporator increases which causes the temperature to increase also.
Eventually the pressures equalize.

If you turn the temperature control up before turning off the A/C you reheat
the dehumidified air. If you hadn't done it in a while you will get a funny
smell from the heater core but it should be a dry smell. If you get a humid
foul stench, that would indicate the compressor is turned off and the
condensate is re-evaporating into the air. Bad smelling evaporators are a
chronic problem in the industry. Just ask Avi Meron.

It doesn't harm the system to turn it off with the car. The idea of turning
up the heat before shutting it off to prevent it from smelling is a new one
on me. Maybe it works.

Bob Cummings
87 Coupe GT

At 10:39 AM 3/12/99 -0800, you wrote:
>While we're on the subject - I'd like to throw this one out:
>
>I don't pretend to understand all the inner workings of Air Conditioning
>systems, but I started trying out the following procedure while using the AC
>and observed the following:
>
>After running the AC for any duration, I noticed considerable hissing and
>such from under the dash upon shutting the engine down.  I'm assuming this
>is condensation being cooked off by the system.  I tried experimenting with
>turning the temp control to the hot side before shutting the car down and
>found that it pushed out a lot of humid, fairly foul/stale smelling air, and
>then went away shortly thereafter.  I theorized that I was accelerating the
>release of condensation and such from the system.  After repeating this
>several times over several days, I found that the smell gradually got
>better.  Is there any merit to this procedure, or is it doing any harm/good?
>It seemed to me that just shutting off the AC at the same time you shut down
>the engine would ensure that the cold components would frost-up to the hilt,
>rather than gradually warm up and thaw.  Any input/suggestions?
>
>Dan Sinclair
>1988 Audi 90, 68K mi.
>Photo and details online at:
>http://131.107.68.28/a4.org/registry/details.asp?car=761
>