Re: 1st Snow in My A4 (1/2 long)

[marriott@Summa4.COM]

Greetings,

> Well, we just had our first snow here in the good old northeast US of A
> and I must tell you, I was looking forward to taking my 97 A4Q out to
> play.

I was involved with the same storm. Hakka 10s to the rescue!! (and a generator; 72 hours 
and counting with no electricity)
 
> But that's not all, folks. The heavy and moist air fogged up all the
> windows within 2 minutes of when the auto-heat came on. "No problemo," I
> though and pushed the AC button hoping to dehumidify the air. But noooo:
> Hanz und Klaus back in Bayerwaldenburgenstrasse decided I 'vil not need
> aircondition im Vinter!' Completely fogged up, I almost went off the
> road. 
> Wow, what a safety feature!

Couple of problems here.

Problem 1.
Humidity in car (due to breathing, sweat, drying of wet clothing)

Solution 1.
Dehumidify air. Run compressor. ==> Problem 2

Problem 2.
Compressor won't run below ~35F/2C.

(Reasons:  Air holds little moisture below ~40F, and virtually none below 32F/0C. No 
water ==> nothing to dehumidify ==> no need for compressor. Also, if the evaporator, in 
the car, gets below 32F/0C, any moisture around will _freeze_ to the coils, negating 
their operation and possibly damaging the coils via expanding ice.)

Solution 2.
Disconnect outside temperature sensor. Allow compressor to run all the time. ==> Problem 
3.

Problem 3.
AC system won't work well as the temperature drops. This is just a function of the 
refrigerant, the laws of thermodynamics, and system design. System may ice up or be 
damaged.

Solution 3.
Make sure you're not on recirc. On my '87 4kcsq (no climate control and about 47 
generations from an A4Q) the recirc flap closes anytime the AC switch is actuated, 
_whether the temp is too cold for the compressor or not_. So, if it's, say, 38F outside 
and the compressor won't run, and you (or at least I) hit "defrost/AC," you can actually 
make the problem 
worse--the flap closes and puts you into recirc, so the inside air gets wetter and wetter 
. . . but no compressor and dehumidification.

Below 32F/0C, air holds virtually _no_ moisture. Below about 40F/4C it's darn close to 
nothing. You can still have 100% humidity, but the amount of water required for that is 
nearly zero. Best results come from just running the heat with "fresh/vent" selected, if 
that's an option, and the fan on medium speed. Keep blowing the wet air out and sucking 
in nice dry air from the outside (Bob D', NO!). Once the "fog" turns to "frost" on the 
inside of the glass, you're 
pretty well done for. The heating system doesn't have the oomph to warm the windows above 
the freezing point, so you're basically waiting for the frost to sublimate. Try to be 
proactive:  when picking up passengers, kick the rear defrost and fan on _before_ they 
get in. That way the system never gets behind--it just has to keep up.

hth,
James