[V6-12v] AC running not so cold

[Tom Christiansen]

Kent,

I rebuilt the compressor on my 1994 90S two years ago. Or actually, I
took a used compressor and fitted the clutch unit from my old
compressor on it. I looked into how the AC system worked then. Here's
what I remember:

On my car, the AC is charged on the high-pressure side (at the
condenser). Audi converted from R12 to R134 in the early 1990'ies.
There's a sticker under the hood (or on the inside of the hood) that's
supposed to tell you if your car has R12 or R134. You can also check
the labeling on the compressor, though, I forget if those are visible
when the compressor is mounted. The fittings for R12 and R134 are
different so if it has been converted to R134, it'll have R134
fittings.
R134 is a much smaller molecule than R12 so you'll definitely need new
O-rings. I believe the compressor and receiver/drier are also
different.

There are switches everywhere that'll turn the compressor off at
various conditions. Too high pressure in the AC system. Too low
pressure. Exterior temperature below about 5C/40F or so. As well as
the load reduction relay cuts out the compressor. It's not a
complicated system, but it does help to have a schematic. Check your
Bentley manual...

If the compressor clutch engages when you turn on the AC, the system
is probably OK, but needs a recharge. If the compressor doesn't turn
on at all, you can have a shop check it out. They usually charge the
system with half a pound of R134 to check for leaks. That would give
you enough to figure out if the system works or not.

The weak spot on the 1993-95 B4 is the evaporator. With UV die, check
for the die around the evaporator drain (above the passenger side
exhaust pipe by the wheel well).

When I got my 1994 90S, the AC didn't work at all and the compressor
had ground itself to pieces. I changed the compressor, receiver/drier,
and orifice tube, and had the system recharged. It's working fine
today.

BTW, the system takes PAG46 oil. You'll need this when you take it apart.

Tom

On 5/27/07, Kent McLean <kentmclean at comcast.net> wrote:
> When I bought my '94 100 S Avant, the AC worked fine. It wasn't ice cold,
> but it was cold. Now, 3 years on, it doesn't blow cold, and summer is here.
> My new-to-me '91 200 20V Avant, on the other hand, didn't blow cold or
> even cool when I got it. So...
>
> - Is there a good on-line tutorial for how automotive AC works?
> - Does my '94 have a low-pressure valve for adding R134a? (I know
>   some Audis only have a high-pressure valve.)
> - I don't know that the '91 has been converted to R134a. Will a
>   cheap R134a conversion kit let me use R134a? Or do I need to
>   change things (hoses, compressor, etc.)?
>
> The '94 is a non-automatic climate control. Yup, it has 3 big
> old-fashioned knobs :) So debugging its system using the CC
> won't work there.
>
> Thanks,
>
> --
> Kent McLean
> '91 200 TQA #1, for sale
> '91 200 TQA #2, no name yet
> '94 100 S Avant, "Moody"
> '89 200 TQ, "Bad Puppy", up in smoke
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