Audi A3 AC System Complete Failure: Fix Guide

As someone with some AC repair experience, I dealt with a similar issue on my 2012 Audi A4 last summer. The symptoms were nearly identical, complete HVAC system failure and warning lights. After taking it to a workshop, they diagnosed a faulty AC control unit rather than an AC compressor issue. The control unit is the electronic brain that manages the entire cooling system. The repair involved replacing the control module and recharging the auto refrigerant. Total cost was 980 Euro including parts, labor, and fresh refrigerant. While expensive, it fixed the problem completely and the car air conditioning has worked flawlessly since. Before committing to repairs, could you share: Have you noticed any refrigerant leaks under the car? Does the AC compressor clutch engage when starting the car? What specific error code did your diagnostic scan show? Is there any unusual noise when trying to activate the system? This information would help determine if your issue is identical to what I experienced or if you might be dealing with a different component failure in the cooling system.

Thanks for sharing your experience. My current mileage is 128113 KM and last service was 3 months ago. The automotive cooling system started acting up suddenly with no warning signs. I checked underneath, no visible refrigerant leak anywhere. The compressor clutch does not engage at startup, and the error code reads P0645. When I try activating the system, there is a faint clicking sound from the front of the engine bay. This issue really concerns me since summer is approaching and a vehicle HVAC repair could be costly. I am hoping it is just a relay or fuse rather than a full compressor replacement.

Thanks for those additional details. Unlike my control unit issue, the P0645 code and symptoms you describe, especially the non-engaging clutch and clicking sound, point more towards an AC compressor circuit problem. Based on the auto refrigerant system diagnostics in my case, here is what you should check first: 1. The compressor clutch relay and fuse, the clicking suggests these might be the culprits 2. The clutch coil wiring, look for any visible damage or loose connections 3. The compressor clutch gap, it may need adjustment In my situation, even though the final fix was the control unit, the workshop first checked these components as part of their air conditioning repair process. The full AC compressor replacement I initially feared would have cost around 1500 Euro, but your symptoms suggest you might get away with a much simpler fix. Since your car was serviced recently, contact the service center. They might have overlooked something during the maintenance that could be causing these car air conditioning issues. Sometimes the AC unit issues can be traced back to recent work done on the vehicle. Would you mind checking if the clicking sound changes frequency when you adjust the AC temperature settings? This detail helped diagnose my problem.

Thanks everyone for the helpful replies. I did some further checking based on your suggestions. The clicking sound stays constant regardless of temperature settings. I called the service center and they confirmed they didnt touch the auto AC system during the last service. I checked the fuses and found one labeled AC COMP that looks slightly discolored. The vehicle HVAC system being so critical, I have scheduled an appointment with a certified workshop for next week. They quoted 180 Euro for initial cooling system diagnostics which seems reasonable. Really hoping its just the fuse or relay causing the AC compressor circuit problems rather than needing a full replacement. Will update once I get the final diagnosis and repair completed. At least I know what to expect cost-wise if it turns out to be something major like in your cases.