jackeroo

One day turned the aircon on only to have it turn off by itself after about 5 min and would not come back on.

Took it to the garage and they topped up the gas and looked for leaks but found none. They ran the AC for a few min before it turned off by itself and would not come back on again - just like with me.

As I drove the car back home from the garage the AC was on for those few min but it seemed to be SUPER aggressive - much more than when I brought it into the garage that morning! Of course it turned off still about 5-8 min after it having come on, but while it was on it was just plain nasty. The kick of the AC was much more noticeable and there was an AC hissing sound coming from the vents when the compressor kicked in. What could they have done to have caused this? - Or is this normal after having the gas recharged on the AC system?

It used to come on very smoothly ... now it's too damn noisy with loud humming when going 40km/h or faster and clicking noise coming from the dash when the compressor engages and disengages.

So now I have 2 issues ...
1. The AC does not remain on for more than 5-8min at a time. (Original issue)
2. The AC now is too full-on while it is on! (New issue)

jackeroo

I wanted to put some details about the first and original issue, so here is how it goes ...

- Start the car in the morning. Climate Control is on Auto and AC "snowflake" comes on.
- AC "snowflake" turns off after 5-8 min. No changes were made to the Climate Control settings. Pressing Auto does not bring back the AC "snowflake". Pressing the AC "snowflake" button makes the "snowflake" appear for a second before it disappears again.
- Arrive at destination and turn off car.
- Get in car about 10 min later and start engin. AC turns back on for a few min before turning off like before.

Hope that helps...

jackeroo

Issue update: I took the car back to the garage and they bled the AC system. I started the car and turned on the AC - no more agressive behaviour, but it still turns off after a few minutes.

The mechanic initially said that for sure the compressor was shot and needed replacing, and then as I explained more of the symptoms he said it could be a couple other things ...

Anyone have any more insight into what might cause these issues?

1. When AC system is drained of gas or full makes no difference on the amount of time the AC remains on.
2. When AC system is recharged with gas it runs (for thsoe few minutes) very aggressively.

jackeroo

So I checked the AC fuse and it seemed fine, but just to be sure I replaced it. - Still no change to the initial issue.

So I am wondering:

- If there is too little or too much gas in the AC system can this cause the AC system to switch off after a few minutes running?
- Can overcharging the AC system cause it to run very aggressively?
- Is there anything else that would cause the AC system to shut off after running a few minutes? ... a bad relay perhaps? ...
- Is there anything I can check myself? (Without unscrewing anything)

Also, when checking the pressure of the AC gas doesn't the engine and AC system have to be on in order to get accurate readings? Reason I am asking is because when I took the car in this morning and the mechanic checked the pressure he did so without starting the engine ... he said his gauge was reading very high pressure!

What about this thing called the "thermal expansion valve"? Could this be the cause of these AC issues?

4Driver4

After the overfill fiasco, the first thing I would do is have the system evacuated and refilled with the correct charge. Sounds like the shop you used is guessing.

After that, use VAG-COM to check for fault codes, run output tests and check measuring blocks for correct operation. You are going to need a Bentley manual and a VAG-COM to fix this car...or a shop that knows more about Audi.

twentysevenlitres

Your A4 doesn't use a thermal expansion valve.
It uses an item called an Orifice Tube.
It's a much more efficient device which offers a restriction between the high and low pressure sides to create the pressure differential.

You could try replacing it - it's relatively inexpensive but requires the system to be evacuated to replace it. You'll find it inside a coupling under the battery.

Provided you can find an air con guy who can put the correct pressure in the system, that would rule out your high/low pressure theory.

After that, I'd be looking at the Climate Control Module.

AudiMick

Confused.

You need to add the Model and year to your profile, your location is important too. Several posters here are in the Southern Hemisphere.

Jackaroo sounds Aussie to me but I am not sure you should be seeing snowflakes at this time of year.

The snowflake comes on if the outside air temp is under 40F. That's the sensor behind the front bumper.

The AC should not run at all if this happens to stop it freezing up and damaging the system.

There are several sensors and interlocks than can mess with you.

You can run diagnostics on the climate control unit to see what the various sensors are reporting back to the climate control head unit.

twentysevenlitres

Good Point!
It is getting warm down here...

I was assuming he meant the snow flake on the Climate Control unit, which illuminates when the aircon is active.
The cold weather Snowflake - which is the frost warning - illuminates on the DIS.

So clarification would be in order...

Depending what year the B5 is, it may not have a DIS too (central dash screen).

AudiMick

Yeah it's terminology, in the US owners manual snowflake is basically a black ice warning.

Black Ice seems unlikely at this time of year for even a place like Hobart.

jackeroo

Sorry guys ... for some reason I got no emails alerting me to the replies here ... good thing I checked!

So the car is a 1998 Avant A4 2.8L Quattro.

The snowflake I talked of was the one on the LCD console between the driver and co-driver seats - I have never seen a snowflake on my console above the steering wheel.

Sorry also if I was not clear enough when say that "I took the car back to the garage and they bled the AC system." - what I meant was they hooked it up to a machine that sucked out all the gas in the AC system.

I have made an appointment with an Audi garage for the 10th of December when they will check out the AC issue.

I appreciate any clues as to what is going on. I sincerely hope it's not the compressor gone bad.

Oh, and I live in Switzerland ... and it's about 1-5C during the day here

Jackeroo sounding Australian - your right - I lived there for 7 years.