VW Sharan AC System Failure: Compressor Diagnosis Needed

I had a comparable issue with my 2003 VW Touran diesel last summer. Having some experience with A/C repairs, I initially thought it was a simple refrigerant leak. The symptoms were identical, A/C completely stopped working, and diagnostic codes pointed to an electrical issue. After taking it to my regular workshop, they found the root cause was an undervoltage problem affecting the A/C compressor. The low voltage was causing the pressure switch to cut off the compressor as a safety measure. The total repair cost was 240€, which covered: System diagnosis, Electrical system check, A/C pressure switch replacement, General A/C system inspection The fix took about 3 hours. Since then, the A/C has worked flawlessly. The belt tensioner was also checked during the repair as it can sometimes contribute to A/C compressor issues. To help diagnose your case more accurately, could you share: What specific error codes you're getting? Does the compressor clutch engage at all when starting the A/C? Have you noticed any unusual noises before the system stopped working? When was the last time you had the A/C serviced?

Thanks for the detailed response. The error codes I'm getting are P0531 and P0535. Last service was done 2 months ago during regular maintenance at 73000km. The compressor clutch definitely does not engage when starting the AC. No unusual noises noticed before failure. Based on what you mentioned about the pressure switch, I checked the AC relay and found it gets quite hot during operation. This could point to an electrical issue affecting the relay switch rather than a refrigerant leak. I'll have the voltage at the AC relay tested first since that seems less expensive than a full system diagnosis. Did your repair also include testing the relay circuit specifically?

Thanks for those additional details. Yes, my repair actually included checking the relay circuit, its a common failure point in these VW AC systems that can cause the compressor clutch to stop engaging. In my case, after finding the hot relay, the workshop tested the entire relay circuit and discovered the AC relay was drawing excessive current, similar to what youre describing. The overheating relay was causing intermittent voltage drops in the control circuit, preventing the compressor clutch from engaging properly. The AC relay replacement was actually done before checking the pressure sensor, and it resolved most of the electrical issues. The workshop tested the new relay operation under load to confirm proper voltage to the compressor clutch. Your error codes P0531 and P0535 are very similar to what I had, typically indicating AC pressure sensor circuit issues. Quick tip from my experience: have them check the fuse box connections around the AC relay while theyre at it. Poor connections there can cause similar symptoms and might save you a second repair visit. Good call on checking the relay first. Based on the identical symptoms and error codes, youre likely dealing with the same electrical issue rather than a refrigerant leak or mechanical compressor problem.

Thanks for sharing those insights. The error codes P0531 and P0535 paired with the hot AC relay definitely point toward an electrical problem rather than something mechanical or a refrigerant leak. I called my regular shop and explained the symptoms. They agreed checking the AC relay and its circuit should be the first step. They quoted 85€ for initial diagnosis and testing of the relay switch plus labor. If the relay needs replacement, parts would be another 60€. What surprised me is they mentioned finding a hot relay is very typical for these VW HVAC systems from that era. Apparently the original relay design tends to develop high resistance over time, causing the overheating issue. Makes sense why the compressor clutch isnt engaging, the relay is probably cutting power to protect itself. I scheduled the repair for next week. Will update once I know if replacing the relay fixes the issue. Based on the matching symptoms you described, Im hopeful this will solve it without needing more extensive repairs to the compressor or having to deal with a refrigerant leak.