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

[Elliott Potter <epotter@abraxis.com>]

Robert Houk - WorkGroup Server Firmware wrote:
>    >Case in point -- recirc. IT WILL NOT LET ME SELECT RECIRC WHEN I
>    >BLOODY WELL WANT IT. It's 37F outside, it will not let me have a
>    >recirc mode to shut out that noxious odious truck (dead skunk,
>    >whatever) for even a few seconds.
>    >
>    >Case in point -- defog. Worse, it's 37F outside, snowing/raining,
>    >humid as a tropical jungle, windows are dripping condensation, and it
>    >refuses to allow the A/C (and recirc) on to dry it out. Hell, even ye
>    >olde UrQe would allow me that option (granted, I had to run max A/C to
>    >dry it out, then switch to max heat to make it not so cold [note: I
>    >don't say "warm"], repeat; but at least it *could* be done).
> 
>    A couple of points here. You definately do not want recirc to dry the car
>    out. Even cars with manual recirc buttons default to outside air when
>    defrost mode is selected (at least all the ones I know about).
> [...]
>    You would, however, like the compressor to run at 37F but there is a
>    technical problem here. There is a switch in the system to keep the
>    evaporator from going below 32F or ice will form and block the air flow. The
>    problem is, once the compressor has turned off at 32F the temperature must
>    climb back to about 40F before it comes back on. You might say "Well, let is
>    come back on at 34F". If it did, the clutch would cycle so often if would
>    not live very long.
> 
> Obvious solution -- put the evaporator downstream from the heater core,
> then when it's cold, you're blowing heated air over the evaporator, so
> it won't ice up, just pull the moisture out of the air. Then you can
> use the "A/C" to dry out the car even at 10F.
 
Or perhaps let you turn on the compressor if the recirc. is closed--so
you're recirculating cabin air, which is warmer, and not getting the
outside air that's too cold.

>    Not all systems are cycling clutch but all have a device to prevent
>    operating below freezing. Hence, the same problem with differential temperature.
> 
> The A4 is (according to my salesdroid) equipped with a variableschmariable
> compressor which is always on, but load-varying, or some such thing.
 
Yea:
"The refrigeration system has a variable displacement air conditioning
compressor.  This compressor is similar to the version used on other
Audi models and automatically adjusts its displacement and output to
match the thermal loads of the A/C system.  The A/C compressor does not
cycle when the A/C system is switched on.  This eliminates surging,
results in more constant A/C pressures, and takes less power to
operate."
And the heat exchanger is the last step in the CC system: you get
recirc. door -> blower motor -> evaporator -> heat exchanger -> vents.


>                                         -RDH

-- 
Elliott

There is a very fine line between "hobby" and "mental illness."