VW Scirocco AC Failure: Relay vs Pressure Switch Fix

As someone with moderate experience working on VWs, I had a very similar issue with my 2010 VW Golf TDI. The HVAC system symptoms were identical, no compressor engagement and AC not cooling. After getting fault codes checked, my workshop found that undervoltage in the electrical system was causing the A/C compressor and relay switch to malfunction. They ran a complete diagnostic on the AC relay and pressure sensor circuits. The root cause turned out to be voltage fluctuations affecting multiple components in the HVAC system. The repair involved: Testing the AC relay functionality, Checking pressure sensor readings, Verifying proper voltage at the A/C compressor, Replacing faulty electrical components Total cost was 240€ and the AC has worked flawlessly since the repair. To help troubleshoot your case more accurately, could you share: What specific error codes you received, Whether the AC compressor makes any noise when trying to engage, If you notice any electrical issues with other systems, Current refrigerant pressure readings if available This would help determine if your Scirocco is experiencing the same underlying electrical problem or if its a different AC component failure.

Thanks for the detailed explanation of the electrical diagnosis route. My issues started quite suddenly last week. After getting it checked, error code P0531 showed up, pointing directly to the AC pressure sensor circuit as the likely culprit. The workshop also confirmed the belt tensioner looks fine and the compressor does spin freely when manually turned. The AC relay clicks when the system is turned on, but the compressor never engages. This seems to match what you experienced with the electrical system, though in my case the voltage readings appear normal when tested. Last routine service was completed at 118000km, about 3 months ago, which included a basic HVAC system inspection. Everything worked perfectly until now, so I am leaning towards a sudden component failure rather than a gradual issue. I will have the pressure switch and sensor circuits tested more thoroughly based on your feedback. The systematic approach your workshop took makes a lot of sense for proper diagnosis.

Thanks for those additional details about your Scirocco. Since I went through almost the exact same symptoms with my Golf, I can share some specific findings that might help. After my initial electrical diagnosis, we actually discovered that while the A/C compressor was spinning freely like yours, the pressure switch was sending incorrect signals to the control unit. Even with normal voltage, a faulty pressure switch can prevent the system from engaging properly. In my case, replacing just the pressure switch did not solve the issue completely. The real fix came when we found that the connection between the pressure sensor and the A/C system control unit had developed corrosion, causing intermittent signal problems. The complete repair ended up requiring: New pressure switch at 85€, Cleaning and resealing electrical connections, Recalibrating the A/C system sensors If your P0531 code persists after checking the pressure switch, look closely at the wiring harness and connections. In these VW models, the connection points can deteriorate over time while the components themselves remain good. Given your mileage and service history, this matches the typical failure pattern I experienced. A sudden failure often points to electrical connections rather than mechanical wear in the A/C compressor itself.

Based on your experience with your Golf, I will definitely have them focus on the pressure sensor wiring connections rather than just replacing parts. The similar error code and symptoms make me think we are dealing with the same underlying issue. Had the car in the shop today for a more detailed diagnosis. They confirmed the A/C compressor spins freely and the relay switch clicks, but found some visible corrosion on the pressure sensor connector, just like you described. They are ordering parts now and quoted about 180€ for the complete repair including labor. Once they replace the pressure switch and clean up all the connection points, they will test the entire A/C system operation before reassembly. I will make sure they check and recalibrate all the sensors as you suggested to avoid any lingering issues. Really appreciate you sharing the detailed breakdown of your repair process. The systematic approach to checking both components and connections helped narrow down exactly what needs attention on my Scirocco. Will update once the repair is completed in case it helps others with similar AC system problems.