Audi Q3 AC Failure: Common Compressor Issue & Fixes

Having dealt with similar automotive cooling issues on my 2014 Audi Q5, I can share my experience. The symptoms were nearly identical, complete AC failure, warning lights, and error codes. After initial diagnostic tests, the workshop found the AC control unit was defective, not the compressor as initially suspected. The entire auto AC repair took about 6 hours. The total cost came to 980 Euro, which included the new control unit, labor, and a system recharge. The repair process involved: 1. Full diagnostic scan 2. Removal of dashboard components 3. Control unit replacement 4. System pressure testing 5. Refrigerant recharge 6. Final testing of the cooling system To provide more specific guidance for your air conditioning repair, could you share: What error codes are you getting? Does the fan still work when you turn on the AC? Have you noticed any unusual sounds when trying to activate the cooling system? When did the problem first start, was it gradual or sudden? This information would help determine if your issue matches what I experienced with my Q5s AC unit issues.

Thanks for sharing your experience. I just checked my service records, last maintenance was at 151000 KM with a routine inspection. The AC failure happened suddenly during a hot day. I hear a clicking noise when engaging the air conditioning, but no compressor engagement. My error code reads P0645 which points to the AC relay circuit. No sounds from the cooling system at all, though the ventilation fan still works normally when selected. After reading your post, I wonder if having the control unit checked first might save time before assuming its a compressor failure. Not looking forward to those repair costs, but better than risking a complete refrigerant leak or bigger AC compressor damage. Did your mechanics mention if they found any relay issues during their automotive cooling system diagnosis?

Thanks for those additional details about your Q3. My situation with the Q5 actually started with similar symptoms, that same clicking sound without compressor engagement. The mechanics did check the relay circuit during the diagnostic phase since error code P0645 often signals relay problems. However, in my case, while the relay was functioning correctly, the control unit was sending incorrect signals, causing the relay circuit error code. A key difference I notice is that my issue developed gradually over a few weeks, while yours was sudden. The sudden failure combined with that specific error code suggests your AC relay might actually be the culprit, unlike my control unit problem. The good news is that an auto AC repair involving just the relay would be significantly cheaper than my control unit replacement. Before any major air conditioning repair work, ask them to specifically test: 1. The relay itself 2. Power supply to the relay 3. Refrigerant pressure switches 4. Wiring connections My total repair ended up being expensive at 980 Euro, but a relay replacement should cost closer to 200 Euro-300 Euro including labor and testing. Make sure they verify no refrigerant leak exists before proceeding with any repairs. Looking back, starting with the simpler relay diagnosis would have been smarter in both our cases before assuming larger component failures.

Thanks for the thorough feedback about the repair approach. That price difference between a control unit and relay repair is significant, 200 Euro versus 980 Euro makes me feel more optimistic about the potential costs. The vehicle HVAC issues do seem to align more with a relay problem given the sudden failure and that specific error code. I will ask the workshop to focus on testing the relay circuit and connections first before exploring more expensive fixes like the AC compressor or control unit. Interesting that your automotive cooling problem developed gradually while mine failed suddenly. That difference in failure patterns does suggest different root causes. I will get the car checked tomorrow and insist they start with the simpler relay diagnosis rather than jumping to major component replacements. Will they need to deal with the car air conditioning refrigerant during a relay repair, or is that system left sealed during this type of electrical fix?