RS3 A/C System Failure: Compressor Diagnosis Guide

I had a very similar issue with my 2019 S3. As someone with some experience working on cars, I first thought it was the A/C compressor too, but it turned out to be an undervoltage problem affecting the entire air conditioning system. The pressure switch and pressure sensor were showing faulty readings due to insufficient power supply. After taking it to my regular workshop, they diagnosed the problem using specialized diagnostic equipment. The A/C system was actually fine, but the electrical system wasnt providing enough power for proper operation. The repair involved: Full electrical system diagnostic, Replacing a faulty voltage regulator, Recalibrating the pressure sensor, Testing the A/C system operation Total cost was 240 Euro and the air conditioning has worked perfectly since then. To help diagnose your specific case, could you share: Any warning lights on the dashboard? Does the belt tensioner seem to be working normally? Have you noticed any other electrical issues like dim lights or slow starter? When exactly did the problem start, suddenly or gradually? Getting this info would help determine if youre facing the same electrical issue or if its actually the A/C components.

Had my vehicle serviced at 73930km and just wanted to follow up on this issue. After reading your detailed response, I checked for electrical problems as suggested. You were spot on, it turned out to be an AC relay switch failure rather than a compressor issue. The technician found no refrigerant leak, which was a relief. The symptoms matched perfectly, no power to the A/C system and complete failure to engage. The belt tensioner was in good condition, and there were no other electrical problems. The fix was straightforward, replacing the failed relay switch restored full functionality to the A/C system at a much lower cost than a compressor replacement. Total repair came to 180 Euro including diagnostic time. Really appreciate the guidance that helped narrow down the problem.

Glad to hear you got it sorted out and that it was indeed an electrical issue rather than a mechanical one! Your symptoms were nearly identical to what I experienced. The relay switch is often overlooked when diagnosing HVAC system problems, yet its such a critical component for proper A/C operation. Your repair cost was actually lower than mine since you caught it early and didnt need the additional voltage regulator work. Its worth noting that keeping the relay switch functional is essential for protecting the A/C compressor from damage, a failing relay can sometimes cause compressor cycling issues. The fact that there was no refrigerant leak is definitely good news, as that would have required a more complex repair process with system evacuation and recharge. For future reference for others with similar issues: A failed relay switch often causes complete A/C system shutdown, Always check electrical components before assuming mechanical failure, No refrigerant leak usually indicates an electrical rather than mechanical issue, Professional diagnosis is key for accurate troubleshooting

Thanks for the thorough follow-up on my case! After reviewing all responses and getting my car fixed, I wanted to share that the A/C relay switch replacement completely resolved the issue. The repair was much simpler and cheaper than I initially feared when suspecting A/C compressor problems. For anyone else facing similar air conditioning system failures, definitely check the electrical components first. The relay switch turned out to be the culprit in my case, causing the entire A/C system to stop working. The pressure switch readings were fine, and having no refrigerant leak was a huge relief. Final repair cost was 180 Euro, which included: System diagnostic, Relay switch replacement, Testing of A/C system operation The A/C compressor is now engaging properly and the cooling is back to normal. Really appreciate the input that helped point me in the right direction for diagnosing this issue.