Audi S1 AC Failure: Compressor Won't Engage

Having some experience with HVAC system issues, I faced an identical problem with my 2014 Audi S3. The A/C compressor would not engage, similar to your situation. After diagnosis, the workshop found that undervoltage was causing the AC relay to malfunction, preventing proper engagement of the A/C compressor. They performed a complete electrical system check and discovered a failing voltage regulator was the root cause. The total repair came to 240 Euro, which included: Diagnostic testing, AC relay replacement, Voltage regulator replacement, System pressure test, Refrigerant level check Before you head to a shop, could you share: Does the issue happen constantly or intermittently? Are there any other electrical issues present? Have you noticed the headlights dimming? What error code is stored? This information would help determine if you are dealing with the same underlying electrical problem or potentially a different issue with the pressure sensor or refrigerant leak. Worth mentioning that throwing parts at it without proper diagnosis could get expensive quickly, especially with these systems where multiple components can show similar symptoms.

Thanks for the input. Yes, the issue is constant and the error code is P0535. The A/C has not worked at all for about 2 weeks now. No other electrical problems and headlights work perfectly. I just had the car serviced at 167812 KM, and they did not spot any refrigerant leak during inspection. I checked the relay switch and it seems to be getting proper voltage. A mechanic suggested testing the pressure sensor before replacing the compressor, as these can fail and prevent engagement as a safety feature. This makes sense given there are no obvious signs of low refrigerant or electrical problems. Could bad wiring between the pressure switch and compressor cause similar symptoms? Want to explore all options before replacing major components.

Thanks for the additional details. The P0535 code actually points to the A/C temperature sensor circuit, not the pressure switch as initially suspected. Your symptoms align perfectly with what I experienced before getting my S3 fixed. After digging deeper into your case, I would recommend checking the wiring harness between the temperature sensor and the control module before replacing parts. A faulty temperature sensor circuit can prevent the A/C compressor from engaging even when the refrigerant levels and pressure switch are fine. In my case, the wire insulation had worn through near the AC relay switch, causing intermittent connection issues. The repair shop found this during their diagnostic process before jumping to component replacement. Key points to investigate: Wire continuity between temperature sensor and control module, Physical condition of the temperature sensor connector, Proper ground connection at the sensor Since your refrigerant levels are confirmed good and the relay switch is getting voltage, focusing on the temperature sensor circuit would be the logical next step. This repair should cost significantly less than replacing the A/C compressor if the wiring is indeed the culprit. Let us know what you find after checking these areas. Based on the error code and symptoms, I suspect youll find either a wiring issue or faulty temperature sensor.

Thanks for the detailed explanation about the temperature sensor circuit. I had my mechanic check the wiring harness today and found a damaged wire near where it connects to the sensor. The insulation was completely worn through and likely causing the circuit issues. The shop quoted 180 Euro to repair the wiring and replace the temperature sensor since it showed signs of corrosion once they got a closer look. This seems much more reasonable than replacing the entire A/C compressor, which was my initial concern. I will update once the repair is completed, but wanted to confirm this matches what you experienced with your temperature sensor circuit problems. The symptoms and diagnostic path seem very similar. Really glad I checked the wiring before jumping to major component replacement. For anyone searching with similar HVAC system issues, definitely worth checking the wiring and sensor circuits before assuming a bad compressor or refrigerant leak when facing a P0535 code.