BoneMan

I have a 1999 A6 and have a question about what may be kicking the A/C system off (e.g. it turns itself over to 'econ' after about a minute of running).
1) I checked the refrigerant levels (and mind you, ambient is HOT right now - about 100F.) and it was a little low (about 35PSI) I added a little - got it to almost 40PSI. I'll assume that should be enough to keep the low pressure switch from tripping.
--note-- I had a hard time adding it because the compressor kept shutting off, causing the pressure gauge to scream all the way up...wierd...maybe that's normal?
2) I noticed that the AUX Electric Fan (behind radiator) does not kick on. I was talking with the previous owner (and part time mechanic, from whom I borrow the Bentley manual) and he "thought" that the electric fan should come on when the AC is on.
3) I checked the fuses and relays going to the AUX Fan, and those are OK.
4) I have not pulled the plug going to the fan, yet, to check w/MultiMeter - I'm looking for whether or not it should be running w/AC unit (or is it strictly based on temp of the coolant?)

QUESTION: If the electric fan is not coming on - will the car's ECU know it and kick the AC system off?
[if you haven't also guessed, I'm trying to 'fix' the AC system not just troubleshoot the fan]

4Driver4

Don't confuse pressure and level. You checked pressures.


It should be on. Make sure it is securely plugged into the harness near the power steer res.

Put your multi-meter away and start using VAG-COM. Output tests are your friend.

bigdadi

If your temp control is in AUTO & temp setting is low enough, about a few seconds after car started, the aux fan will turn on. Press the ECON, the aux fan should turn off.

Aux fan is designed to turn on for a few criteria. On top of a/c, another example is the coolant temp is hot enough that needs aux fan's assist.

The reason I know this is because I used to have a noisy aux fan, the fan bearing problem. It made noise whenever it turns on.

SloopJohnB@mac.com

static system pressure is generally higher on the low side, lower on the high side.
Sounds like you're measuring low side with engine/compressor running.
Yes, auxiliary fan should be running with ac on. If it's not running you need to check the fan and the fan module, by default.
If the fan runs at all, chances are the fan module is defective although it's possible you have a defective low pressure switch or high pressure switch. What is the high pressure reading? Over 250psi you might have an expansion valve/orifice blockage.

On at least one system I'm familiar with (volvo and saab) there is a filter element just ahead of the expansion valve that does clog up over 5-10 years. On my old 1990 740T volvo the ac was working fine but after 15 years I decided to have it checked...the filter was 60% clogged (3 of 5 sections were clogged/discolored) and mildly restricting refrigerant flow. Replaced the filter and receiver/dryer and sucked/recharged and the thing pulled about 37F on an 80F day.

Sooo, there are common a/c system temperature/pressure diagnostics you could look up on google, make sure you use the temperature/pressure graph for R134a unless you know otherwise, you'll need to catch condenser temp and evaporator temp as well. There are just so many issues here that it's impossible to guess which one is your problem.

SloopJohnB@mac.com

PS...scroll down and see Redneck Trucks issues with aux cooling fan....

BoneMan

Awesome info....Thanks (all). This is my first EuroLuxoCruiser, so I'm just getting familiar with some fine engineering on this beast. I've had rice-burners for many, many years....Even changing the oil on her has been a pleasant experience. Pretty impressed so far.

I think things are homing in on the fan - as it does not come on at all when I put the A/C system on (therefore, can't see if it shuts off when I turn the A/C off )

OK - being a newbie to the world of Audi (or Germanic vehicles in general) - is the term VAG-COM a generic term for the online diagnostics of the vehicle? I have a OBDII USB interface with software for Audi codes and online diag's....haven't hooked it up yet. That's for Saturday. OR....is there a particular "VAG-COM" product that everyone on this forum seems to use? (I see so many references to various things regarding VAG-COM, I'm having a hard time figuring if it's a noun, pro noun, verb, or adjective )

Anyway - I've got an ElmScan5 with OBDWiz software....hope that will work for now....let me know the more "Audi" way of doing things. Thanks!!

One bit of info to note: the previous owner (who has maintained and kept up on all the maint. for the last 7+ years, and before that, dealer maintained) did have to replace the aux electric fan...well, probably about 6 or 7 years ago. I think he used an Audi one.... can ask. Point of failure? Being as though it's 110F right now - it's just hard on everything. (even my check engine light in my SubieWRX just came on yesterday, a first....will have to look at that, too)

BoneMan

I did not see 'RedNeck Trucks' - or did you copy/paste into your reply?

SloopJohnB@mac.com

Redneck Trucks is the poster.
Here's a link:
https://www.audiworld.com/forums/sho...php?p=24053985

LOL--it's an ancient thread that was put in my list by teutonix' posting of an allroad owner's fan module replacement url/tech article link.