Audi A6


I recently purchased a '02 Audi A6 1.9 tdi (96k miles). Everything seemed fine until spring kicked in and the weather became warmer. The climate control does not cool at all. The vents produce air but it is not cold. In fact, pressing ECON (a/c off) gives better results although far from cold air.

I have:

(1) Tried VAG-COM but had too many communication errors to get any fault codes.
(2) Read on the internet how to access the diagnostics on the climate control itself but because it is a dual display, I have not been able to get a definitive list of fault codes to figure out what is wrong.
(3) Had the refrigerant levels checked and they are fine.
(4) no problem communicating with all other control modules in the car using VAG COM without a problem, so I suspected that the air con controller was faulty (previously had heard buzzing sound from unit). I got a replacement climate control display unit and installed but still the problem remains.
(5) I checked all fuses and relays and they seem OK.
(6) When I switch on ignition (without starting engine) and just before the aircon comes on, I can hear a faint clicking behind the dash which seems to be coming from deep inside the dashboard. Could this be the air flap motors malfunctioning?
(7) When the car is running and I check under the bonnet, the refrigerant pipes are not cold at all. Would malfunctioning air flaps cause this?
(8) I ran VAG COM on the replacement unit and still communication errors but repeated my attempts until I got a scan of the unit and found one fault:

Air Quality Sensor - Electric Circuit Failure

I checked the sensor (located in plenum chamber next to pollen filter) and the mount for the sensor was broken (no idea how this happened) with the sensor lying on the bottom of plenum chamber (all connections seemed intact). I have ordered a replacement sensor and waiting on arrival but I would like your opinion on this - I cannot see how this sensor circuit failure could be preventing cold air from circulating (air con seems fine otherwise). Am I wrong? I thought that the problem might be likely due to a faulty pressure switch but VAG COM did not give any other faults.

I would appreciate any advice at all. I am desparately in need of cold air!
April 21, 2007.

Does the A/C clutch engage when the A/C is switched on?

Apr 24, 2007.

Thanks for replying.

As far as I can tell, this compressor has a regulator valve rather than a clutch (?). Could not find any relay for a clutch. In either case, when the a/c is switched on, there is no noticeable load on the engine at all or change in the voltage gauge so I'm guessing that the compressor is not engaging.

Apr 25, 2007.
OK, for those of you that are interested, I solved this problem myself. Here's what I found: 1) Could not get any cold air; checked refrigerant levels and they were OK, ran diagnostic software (VAG COM) but no faults were found.

2) VAG COM has a feature where you can run output tests - tried this and everything seemed to check out, EXCEPT the cooling fan.

3) CHecked the relays and power to the cooling fan and all were fine. Conclusion - the cooling fan was dead.

4) Unbolted the a/c compressor from its mounting. The compressor is belt driven through a pulley. To prevent the compressor shaft being sheared from the sudden torque of an engine start, the pulley is linked to the compressor shaft through a plastic moulding. CHecked the plastic moulding and it was competely worn away - so the compressor was not turning over when the engine was running

5) The cause of the original problem was: cooling fan stops working, condenser does not get cooled properly, increased pressure in the refrigerant circuit, major strain on the compressor drive and the pulley assembly breaks down, resulting in no cold air.

6) I replaced the fan and pulley assembly, and I am back in business

I hope that this information helps someone out there.

Jun 15, 2007.