RS7 AC Compressor Failure: Relay & Sensor Issues

I faced a similar issue with my 2018 RS6. Having some experience with HVAC systems, I can relate to this frustrating situation. The symptoms you describe match exactly what happened to my car. After initial diagnosis, the workshop found that undervoltage in the vehicle was preventing the A/C compressor from engaging properly. The AC relay was also affected by this electrical issue. The repair process involved: Complete system diagnosis, Testing the electrical circuit, Replacing faulty components, Verifying proper A/C system operation Total cost was 240 Euro including parts and labor. The fix resolved the cooling issues completely and the A/C compressor has worked flawlessly since then. To provide more specific guidance for your case, could you share: Current mileage, Any warning lights on the dashboard, Whether the issue started suddenly or gradually, If you notice any unusual noises when trying to engage the AC, Whether the blower motor is still working These details would help determine if your issue is identical to what I experienced or if there might be other factors involved with your refrigerant system.

Thanks for the feedback. My RS7 has 88839 KM on the clock and the last service was completed just 2 months ago. The air conditioning stopped working completely last week without warning. No unusual sounds from the AC relay or compressor area. The blower works fine, but only blows warm air. The workshop found low refrigerant pressure during initial testing, suggesting a potential refrigerant leak somewhere in the system. When cycling the AC on/off, you can hear the relay click but the compressor doesnt engage. This happens consistently every time.

Thanks for providing those additional details. The symptoms on your RS7 actually differ from what I experienced with my RS6, despite seeming similar at first. While my issue was electrical, your case sounds more like a classic refrigerant leak, especially given the low pressure reading and relay clicking without compressor engagement. The pressure switch is likely preventing compressor activation as a protective measure. In my RS6, after the initial electrical fix, I actually encountered a similar refrigerant issue about 6 months later. The repair involved: Leak detection with UV dye, Fixing a small leak at the AC line connection, Replacing the belt tensioner which showed wear, Recharging the system to proper pressure levels The total repair came to 480 Euro including the refrigerant charge and new components. The pressure switch and AC relay were also tested but were functioning correctly. Before you proceed with repairs, have the workshop perform a proper leak test. The clicking relay with no compressor engagement strongly suggests the pressure switch is doing its job by preventing compressor operation under low pressure conditions.

Based on all these helpful replies, it seems my AC issue is indeed related to a refrigerant leak rather than an electrical problem. The pressure switch protecting the A/C compressor explains why I hear the relay click but get no compressor engagement. Looking at my service records, the AC system has never needed a recharge before, so a leak developing after 88000 KM seems reasonable. Going to schedule a proper leak detection test this week. If the repair cost is around 480 Euro including parts and labor as mentioned, that sounds fair considering the work involved. The most important thing is identifying the exact location of the refrigerant leak before just recharging the system. Will update once the workshop completes their diagnosis, but for now I appreciate the guidance in narrowing down the likely cause. Having the belt tensioner checked during the repair also makes sense as preventive maintenance.