Audi A3 HVAC Failure: Compressor Issues Diagnosed

I had a similar issue with my 2015 Audi A4 last summer. Having some experience with HVAC systems in cars, I first thought it was just low refrigerant, but it turned out to be more complex. The workshop diagnosed an undervoltage problem affecting the relay switch controlling the AC compressor. The system was shutting down to protect itself. They found the root cause was a failing pressure sensor that was sending incorrect signals to the control unit. The total repair came to 240 Euro, which included: Diagnostic scan, Pressure sensor replacement, New relay switch, System testing Before the fix, my symptoms matched yours exactly, no cooling, AC not engaging, and error codes. The repair completely resolved the issue and the air conditioning has worked flawlessly since. To better assist with your specific case, could you share: What error codes are showing up? Does the AC compressor make any noise when you try to engage it? Have you noticed any other electrical issues? When did the problem first start? This information would help determine if youre dealing with the same underlying issue or if its something different with your A3s HVAC system.

Thanks for sharing. My car has 179977 KM and just had a maintenance service 2 weeks ago. After getting a second opinion from another workshop, they found the AC relay was indeed faulty, but also discovered a significant refrigerant leak near the compressor connection. The system pressure test confirmed the leak. When they repaired both issues, replacing the AC relay and fixing the refrigerant leak, the air conditioning started working properly again. Total cost was 320 Euro for parts and labor, including a system recharge. The pressure sensor readings are now normal and no error codes remain. If others face similar symptoms, I recommend getting a proper pressure test done before assuming its just a compressor failure.

Thanks for the update on your A3. This matches my experience exactly, these HVAC system issues often involve multiple connected problems. After fixing my A4s relay switch and pressure sensor, I also discovered a small refrigerant leak that needed attention. A faulty AC relay combined with a refrigerant leak is actually quite common in these models after around 150000-180000 KM. The vibration over time can loosen connections and cause seals to deteriorate. 320 Euro is a fair price for that repair scope. The diagnostic approach your second workshop took, checking both the electrical components and doing a pressure test, is exactly what helped identify the full extent of the problem. Much better than just assuming a complete compressor failure, which would have been much more expensive to replace. Good point about the pressure test, its a crucial diagnostic step for any air conditioning issue. A proper test can quickly reveal if youre dealing with a refrigerant leak or an electrical problem with the relay switch. Since the repair, have you noticed any unusual sounds when the compressor engages? Its worth monitoring for the first few weeks after such repairs.

I want to provide an update after running the car for a few weeks. The air conditioning system has been performing perfectly since the repair. No unusual sounds from the AC compressor and the cooling is consistent. The refrigerant leak near the compressor connection turned out to be from a worn seal that had gradually deteriorated. The workshop also showed me how the relay switch had visible burn marks, explaining why the HVAC system was failing intermittently before complete failure. For anyone searching with similar symptoms, heres what solved my case: Replacing the faulty AC relay switch, Repairing the refrigerant leak at the compressor connection, Full system recharge, New seals at connection points The 320 Euro repair has proven to be worth every cent. The key was finding a workshop that did thorough diagnostic testing rather than jumping to conclusions about needing a complete compressor replacement. My A3s air conditioning now works as good as new.