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

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

Robert Houk writes...  

>I agree that automatic systems can perform well. In theory. In RealWorld(tm)
>practice, they often fall far short of that.
>
>For example, Audi's suck (HVAC-wise).
>
>Case in point -- the sun sensor. As near as I can tell, it does
>nothing.  (Hey, maybe it's busted?) Every morning as I go into work, I
>have to crank the "smart system" down to 63 to keep from getting fried
>out of my seat (I do tend to like it "cool", this is "winter"
>time). Every night as I go home (sun is down) I have to crank it up to
>68, 70, and even sometimes turn on the seat heat for awhile.  Consis-
>tently.  Daily. Further, I have to manually force center-vents in
>order to warm my pinkies (yes, I could wear gloves...), then -- once
>the interior is more-or-less comfy -- I have to manually shut off the
>center vents to keep the *(@%$#@&)(*!ing thing from blowing *COLD*
>(er, excuse me, "fresh") air on those self-same pinkies.

Whoops!! I wasn't very clear here. The only function I suggested be out of
the driver's hands is the recirc/osa function. IMHO a "good" manual HVAC
control is better than the fully automatic systems. By "good" I mean one
like the typical U.S. road monsters with one lever or knob for mode(where
the air comes from and whether the A/C is engaged), One lever or knob for
temperature and one knob for blower speed. 

You are absolutely right about automatic systems. The ones that have a lot
of engineering and testing behind them work very well. The ones that are
thrown at the vehicle are terrible. I'm not commenting on Audi systems as
the only one I'm familiar with is the prehistoric manual system in my Coupe GT.

Even the good automatics are often misused. My wife drives a 95 Cadillac.
The automatic system is as good as it gets BUT she gets in and dials the
temp to max cold (Texas you know). Then when she gets too cold she dials the
fan speed to low. I've been in this business for more than 30 years and I
can't even get my wife to operate the thing right.

>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.

Not all systems are cycling clutch but all have a device to prevent
operating below freezing. Hence, the same problem with differential temperature.

Bob Cummings
87 Coupe GT