Audi S6 AC Dead: Compressor Warning Signs & Solutions

Had the exact same trouble with my Audi S4 (2002). With some experience working on cars, I initially thought it was an AC compressor issue too, but it turned out the auto AC repair was more complex. The symptoms matched perfectly, no cooling, system completely dead, warning light. After checking the auto refrigerant levels, which were fine, the workshop diagnosed a faulty AC unit control module. The control unit was completely dead, which explains why the entire car air conditioning system stopped responding. The repair took about 4 hours, including testing. Total cost was 980 Euro including parts and labor. Since then, the AC has worked flawlessly for the past 2 years. Before you head to a workshop, could you share: Any unusual sounds before the system died? Does the fan still work when you turn on ventilation? What exactly does your error code say? Have you had any previous AC issues? This info would help determine if you are facing the same control unit problem or if its actually the AC compressor.

Thanks for the detailed info about the control module situation. In my case (104023 KM), I actually did hear some squealing sounds from the front of the engine bay about a week before the automotive cooling system died completely. The ventilation fan still works fine on all settings, which made me think its specifically an AC compressor issue rather than a control module problem. The error code reads P0645 which typically points to the AC clutch relay circuit. Had my last service done 3 months ago but they didnt note any air conditioning repair issues during inspection. Guess I should have paid more attention to those early warning sounds. Has anyone else encountered this specific error code? Really hoping to avoid a full compressor replacement if possible.

Thanks for the additional details. Given those squealing sounds and the P0645 code, your vehicle HVAC issue does sound different from what I experienced with my control module failure. The error code specifically points to the AC clutch relay circuit, which is actually good news, it might be simpler than a full compressor replacement. When my S4s control module failed, there were no warning sounds at all, it just stopped working suddenly. Your car air conditioning symptoms point more toward a mechanical issue, likely with the compressor clutch assembly or its electrical circuit. A squealing sound often indicates the compressor clutch is failing or has seized. In these cases, replacing just the clutch assembly might fix the refrigerant leak and restore cooling, much cheaper than a full compressor replacement. My mechanic recommended checking the clutch gap and electrical connections first before condemning the entire compressor. For reference, a clutch assembly replacement typically costs around 350 Euro-450 Euro with labor, versus 1200 Euro-1500 Euro for a complete compressor job. Its worth having a workshop check the clutch specifically given your symptoms and that error code. Would recommend getting the air conditioning repair done soon, as running the system with a failing clutch can damage other components.

You are completely right about the mechanical signs pointing to a clutch issue. That and the error code make me more confident its likely not a full compressor failure. The squealing sound matches what others described with failing clutch assemblies. Getting it checked soon makes sense, dont want to risk damaging other vehicle HVAC components. The cost difference between just replacing the clutch versus the whole auto AC repair job is significant enough to be worth investigating. Really appreciate the detailed breakdown of typical repair costs too. Will schedule an appointment focusing specifically on inspecting the clutch assembly and refrigerant system. The fact that my ventilation still works properly at least confirms the electrical and control systems are functioning. Hoping a simple clutch replacement will resolve the automotive cooling issues rather than needing the full compressor replaced. Thanks for helping narrow down the likely cause. Will update once I get the final diagnosis and repair completed.