jbrentd

Hello everyone, just wanted to check to see if anyone has any suggestions on an issue I'm having with my A/C. I've been having intermittent A/C issues where it just won't blow cold. It started out just being a problem when I first start up the car and after I started driving, the air would start to blow cold. This had me thinking it was an electric fan or air flow problem, but I haven't had any overheating issues (knock on wood) and it's been pretty hot lately.

The past few days it won't even start getting cold at all. This morning, I used one of those DIY refrigerant hoses that they sell at auto parts stores to check the system pressure. When I first started up the car, I put the A/C on "LO" and the pressure gauge was reading 0 pressure. Must mean the compressor wasn't working, right? I take off for work and the A/C starts working again. Since I had the pressure gauge with me, I checked the reading again and it's right where it should be. That should indicate that I'm good on the refrigerant level, right?

I didn't get any codes on my VagCom for the HVAC system.

Does anyone know what might cause intermittent issues with the compressor? When it's on, it's working great (41 degF air out of the vents). Is there a relay that could be the issue? Or maybe a sensor (I think I remember seeing a plug on the compressor itself)? Or something else that controls the air compressor clutch? Thank, Brent

royclark

How long since you had the air-con serviced? I get mine done every year.

jbrentd

Uhh, never. Haven't had the need to.

I did find a TSB on the Pressure Sensor (G395) stating that the sensor leaks refrigerant. It also states that the wires get pinched, but only in A4/5, S4/5 and Q5 models. Also looked on eBahn at the system overview and plan to check a few things. There's a good write-up on the Ross-Tech forum on some things to check.

Musty

Pressure readings like that might suggest a restriction in the orifice tube--pressure builds up in front of the restriction (resulting in a low reading at the port) then it gets cleared, and things start working normally. Take a look at the diagram for reference: HOSES & LINES. AIR CONDITIONER & HEATER.. Fits: 2007 Audi A6 Base Sedan Quattro 4.2L V8 A/T AWD | Mid Atlantic Audi
That would be bad news for your compressor, receiver/drier, and possibly condenser, so hopefully it's not the case. But it's definitely worth having an a/c service done to confirm this. Not the sort of thing I would recommend doing yourself because if there pressure's where it should be but it's reading low, adding pressure could do more harm than good.

Good luck, and let us know how it turned out!

SchwarzS6

There are some AC diagnostics in the car. Get a VAG-COM scan.

royclark

Q. How often should my aircon system be serviced?
A. Every 18 months to 2 years to ensure it operates at maximum efficiency.

Yours is nine years old and NEVER had a service.
I wonder why it's not working properly.

jbrentd

Ok, maybe it has been serviced, but not in the 3 years I've owned it.

jbrentd

The intermittent nature of the problem is strange. Yesterday evening was the first time (since first posting about this) that the problem has occurred. When I left work for home, I hooked up my Vag-Com and logged the first three groups in the HVAC control module. Group B contains the shut-off conditions for the compressor. It was reading a condition of "0", which means the compressor isn't being told to shut off (i.e. should be running). But it wasn't, as I was only getting a refrigerant circuit pressure reading of 10 bar (145 psi). About 4 minutes later, when I jumped on the on-ramp to the freeway, the refrigerant circuit pressure reading started to rise and settled out at around 27 bar (392 psi). All was good the rest of the way home.

Gonna have to find some time to try a few of the things suggested in this post on the Ross-Tech forum.

Tis’ the HVAC Season

SchwarzS6 - Let me know if there other useful groups I should be watching.