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Re: A/C recirculation/warm air from dash ponderings..
>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).
Depends. I *DO* want recirc when it's 99.9% RH outside. By default,
"A/C" selects recirc on some models (on '83 UrQ, it's forced, you
have no option; on '98 A4 it's selectable, forced on "max"). recirc
will dry the inside faster than non-recirc, almost always. But it's
nice to exchange some of the CO2 for O2 as well . . .
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.
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.