Q7 AC System Failure: Compressor vs Switch Mystery

Using a 2015 Audi Q5 3.0T, I encountered nearly identical AC issues. The initial symptoms were similar, complete AC failure and system errors. While a faulty AC compressor was suspected, diagnostic testing revealed it was actually a combination of problems. First step was checking the AC relay and pressure sensor, as these are common failure points in the HVAC system. In my case, the pressure sensor was giving false readings due to a minor refrigerant leak, causing the system to shut down as a protective measure. The fix required: 1. Testing the AC relay function 2. Pressure sensor replacement 3. Fixing the refrigerant leak 4. Recharging the system The belt tensioner was also showing wear and needed replacement since it affects the AC compressor operation. This turned out to be a significant repair involving multiple components, but still less costly than a full compressor replacement. Worth noting these issues are relatively common in VAG vehicles after 150k km. Recommend having a complete HVAC system diagnosis before replacing the compressor, as the root cause could be electrical or sensor-related. For initial troubleshooting, have the refrigerant pressure tested and the electrical system checked for proper voltage to the compressor clutch.

Thanks for sharing that experience. Had pretty much the same symptoms with my Audi Q7 last summer. The AC stopped working completely and I was worried about a full A/C compressor replacement too. The AC relay ended up being the culprit in my case, it wasnt engaging the compressor clutch at all. After diagnosing the actual issue through proper testing of the A/C system components, replacing the relay switch solved the problem entirely. Really glad I didnt jump straight to replacing the whole compressor. Do you remember roughly what you paid for the full repair on your Q5? Just wondering since prices can vary quite a bit. Has everything been working properly since the fix?

Great to hear you got yours fixed with just the relay replacement! Since getting my Q5 repaired at the shop, the air conditioning has been working flawlessly. The diagnosis showed the main issue was undervoltage in the electrical system, which was causing the A/C compressor to shut off unexpectedly. The total repair cost came to 240 Euro, which covered the electrical system repair and testing of the pressure switch and AC relay. Much more reasonable than a full compressor replacement would have been. Maintaining correct voltage to the A/C system components is crucial, when the electrical supply is unstable, the compressor protection circuits can trigger shutdowns. The belt tensioner was actually fine in my case, so that helped keep the costs down. The pressure switch readings are now consistent and the compressor engages properly every time. No more error codes or system shutdowns since the fix.

Just wanted to wrap up and share my repair experience. After getting tired of unreliable fixes, I took my Q7 to a different repair shop that specializes in AC systems. The technician first checked the pressure sensor readings and tested the AC relay connections before jumping to conclusions. Turns out the problem was actually simpler than expected. The air conditioning system had a minor electrical issue affecting the relay switch. Total bill came to 180 Euro including diagnostic work and parts, way less than the 1200 Euro estimate I got for a compressor replacement at another shop. The AC has been working perfectly for several months now. Really glad I got a second opinion and proper testing done instead of rushing into expensive repairs. Definitely learned my lesson about getting thorough diagnostics first, especially with AC system issues.