bcsangerman

Hi,

I am new to the forum, and new to an 03 Audi S6.

Upon purchasing this low mileage example sight-unseen, I have realized the A/C does not blow cold. Upon some other found issues, this is definitely the first I want to sort out.

I DID SOME RESEARCH!

The controls in the climate control system seem to respond appropriately, however, the compressor clutch does not seem to be engaging. Could be an issue with the compressor clutch or could be low on Freon. I bought a quick DIY R123 bottle and some electrical wire to test the clutch.

The clutch engages when powered directly powered by the battery, and the gauge on the bottle shows Freon as filled at around 35 psig, so I DO NOT HAVE A LEAK.

Upon forcing the clutch engagement with the electrical wire, I am getting cold A/C air inside.

So what should I deduce the issue to be?

bcsangerman

Wowza! Thanks for the quick reply. That is all foreign language to me.

Any literature I should read to catch up on it?

bcsangerman

I appreciate the help, but surely this isn't a forum that just directs people to a manual or shop for answers and assistance.





I have worked on cars my whole life, from 4 cyl Hondas, to Classic FJs, to V12 BMWs. I am, however, new to Audi's as well as Aircon systems.




I'll look into picking up a manual, always good to have, and thanks for the Bentley manual recommendation.

bcsangerman

QUICK UPDATE: I spoke with the previous owner who switched out the HVAC control unit with the current one as the old one had worn out buttons. He said the AC worked with the old one, and never tested after replacing it.

What could be malfunctioning with the new one that is causing the compressor clutch to not engage?

He gave me the old one. If I plug it back in, is there any programming that needs to happen with it or is it plug and play?

Harleyguy

1) A/C functions on Audi is nearly a specialty unto itself and requires some special equipment to properly service. Yes you can often resolve "weak" A/C by adding over the counter refrigerant. 2) Appreciate that you have experience working on various vehicles, however many an experienced mechanic has been stymied by the Audi brand. The Bently Manual is the preferred resource for information on these quirky little things. The number 2 reference is probably Google. 3) In your case the A/C clutch isn't receiving the signal from the control unit that tells it to turn on. Could be many reasons that this is happening (controls, sensors, etc.). In the interest of saving money I would swap the control units back. Not sure if any reprogramming is necessary. If you plan on keeping this car for a while and doing your own work get a VAG Com scan tool to trace down problems. Basic OBD I & II type scanners will only give basic information mostly related to Check Engine Light or similar. Ross Tech is one of the most preferred scan set-ups. Look them up and decide which version fits your needs. Without a VAG specific scan ability you will not be able to look for issues related to ABS, electronic traction control (ESC warning light), auto transmission control module, and other systems on the car. Most of the forum members here have sourced local independent repair shops that have expertise in Audi. It will save a lot of money when you encounter a repair that is beyond your skill level.

bcsangerman

Super helpful. I will be picking up a Ross-Tech Vagcom, as well as a Bentley manual.

I'll plug the old one back in and see what happens.

bcsangerman

I plugged the old one back in and the A/C works; compressor clutch activates.

The original unit that came in the S6 is part # 4B0820043AM, which according to ECS applies to 9 C5 variants, while the "newer" unit that was installed is part # 4B0820043AH, which according to ECS applies to just 4 variants. Although model years are not listed, it might be later models for the unit ending in AM, vs earlier models for the unit ending in AH.

It all plugs in fine and the same, not sure why there is no signal to the compressor clutch with the AH unit.

Needless to say, I will be sacrificing having unworn buttons for cool air this summer.

Claymotion

This may be my problem. I'll look into it soon.

Also, the buttons on the climate control head can be removed and you can put your new buttons in the old CC head.
If you still own the car that is.
Best of luck mate!

4Driver4

[QUOTE=bcsangerman;25312625]I plugged the old one back in and the A/C works; compressor clutch activates.QUOTE]

All of these units are not the same. They may look the same and all the plugs may be the same, but part numbers matter.
BTDT with my old RS6 with worn buttons. I tried several units before finally gutting the original control unit and swapping the electronics into another box.