Bill S

The A/C and defrost have stopped working on my '98 Avant. Can't get cold air no matter what the outside temperature and the compressor isn't coming on when the defrost is activated. For quite a while before this, there was an intermittent mechanical sound, kind of like a cricket, when the blower was on.

My regular mechanic, Shine Racing Service in Walpole, MA, doesn't work on A/C and referred me to the dealer. For obvious reasons, I'd rather not go there.

Does anyone have advice on:

1) what might be wrong

2) whether a good independent shop that handles A/C work could accurately diagnose this without a lot of trial and error

I got the impression from Shine that the dealer may have a specialized scan tool for diagnosing these things. If so, maybe the dealer is the best choice even though I am very suspicious of them based on past experience. If not, I'd rather try a good and comprehensive general repair shop such as Junior Damato's (the "Car Doctor") shop in Hyde Park. Does anyone know for sure?

Thanks for any advice.

JAFO

<ul><li><a href="https://www.audiworld.com/tech/int5.shtml">https://www.audiworld.com/tech/int5.shtml</a</li></ul>

Neo1130

If you have a DVM you can check voltage at the compressor, if there is no voltage continue back to the relay... If there is no voltage at the relay then the signal is not being put out of the control panel which also means a few things...

Fuse #21
You have a bad MAF
Your line pressure is too high or too low
Could have a bad control panel
Intake air temp sensor busted

As of right now those are the things that I can think of off the top of my head that will make the A/C not come on... I'll add to those as I remember...

Bill S

Thanks for the tip! I got the following DTC's (diagnostic trouble code)s from the on-board diagnostics:

5.1
Outside Air (Ambient) Temp Sensor, front, static open
(Oddly, though, the outside temp display is working fine.)

13.7
Footwell/Defroster Flap, sporadic block

22.1
A/C Refrigerant High Pressure Switch, static open
Compressor remains off until switch closes

It would seem that the 22.1 trouble code explains the failure of the compressor to turn on.

Does anyone know how to interpret these codes further? Is this enough for an independent shop to fully diagnose and fix the problem, or is the dealer the only one who will have the proper tools to do a thorough diagnosis?

Thanks in advance!

Bill

Neo1130

switch itself is bad... Remove the passenger side headlight, remove the plug from the side of the condensor, I cannot remember 100% on this but you want to jump pins 1 - 2 and then 3 - 4 you leave open, with the engine running... Make sure you have the A/C set to on...

3 and 4 should be the high pressure which is normally open, so if those close then your A/C will see that as a high pressure fault. 1 and 2 are normally closed under normal operating conditions...

So...

Remove passenger headlight
Find 4 pin plug on condensor and remove
Start car with A/C "on"
Keep hands and tools clear of running engine
Jump pins 1/2, if A/C comes on, replace switch, or better yet, have a shop do it since they have to evacuate the system, purge it and fill it again...

Bill S

Do you think it's pretty certain it's the high pressure switch? I wonder if it could really be 5.1 since the outside temp display is actually working great and since I wouldn't imagine that outside temp would have any effect on defrost anyway.

If it is the switch, does its replacement require removal of the dash, or is it done from under the hood?

I can't thank you enough. It sounds like a good independent shop can probably diagnose and fix this and save me a trip to the dreaded dealer. I have had nothing but bad experiences there myself, and I have heard numerous stories from people who used to work there about how the commission-based service writers blatantly rip off customers on a routine basis. One choice story involved a customer who was charged hours of diagnostic time with a report of no documentable problem found. But he was suspicious based on past experience and had marked his tires; his car had not moved from the lot since he dropped it off! And this stuff, reportedly, is at what everyone around here seems to regard as the best of the local dealers: Clair Audi.

Thanks again!

Bill

Neo1130

But if the sensor goes bad and tells the control panel that it is below 36 degrees then the compressor will not kick in... But I call the switch...

Bill S

Thanks again. I will let you know how it turns out.

If I may, just one more question that occurred to me: do you know how long the system holds onto those codes and if they persist after the error condition clears? For example, could that outside temp sensor code be from a while back? If so, that might explain why that sensor seems to be working fine now.