G2Mike04

Since I have given up on the tranny for now, I decided to move to the next problem on my list: the non-functional a/c.

Car is a 1998 A4 Avant Quattro. When I bought the car the compressor clutch would not engage when you turned on the air. I bridged the terminals on the pressure switch like the manual says to do and the compressor kicked on. Great. I guess that means the control module, compressor, and a bunch of other crap is probably all good. Checked the pressure on the low side and discovered it was a little too low, so I bought a recharge can of R-134a.

It was just ever so slightly low (about 20 psi @ ambient 60 F) so I reconnected the switch and shot a bit in and the compressor kicked on. Great. Switch is good.

However, warm air is still coming out of the vents with the temp set to "LO" on AUTO with the little snowflake. The Auto-HVAC module is not returning any fault codes.

So why am I getting no cool air?

4Driver4

Because there is a leak in the system somewhere. Bring it to a shop and see if they can find it. If they can't, replace the evaporator.

G2Mike04

Got an appointment for Wednesday.

turbo510

When you say 20 psi, was that with the compressor running? The larger aluminum tube by the cabin filter should get cold if there is enough freon to liquify. Too little, and it remains a gas and won't work.

G2Mike04

Yep, after adding the coolant and allowing the compressor to run for a bit the pressure on the low side did not drop. You may be right... I think the one closest to the cabin filter is the high side and I did not have the correct fitting for my gauge to check that one.


By the way, the shop evacuated and recharged the system and added dye. They kept it for 3 days and checked it periodically for leaks and didn't find anything. It now blows nice, cool air :-) Maybe I should have tried shooting in a bit more coolant myself, but when the compressor came on and the low side pressure was correct I figured it was ok. Dunno.