Audi S7 AC Dies: Costly Compressor Drama Unfolds

Had almost the exact same auto AC repair issue with my 2017 S6 last summer. I have some experience working on cars but left this one to the pros since vehicle HVAC diagnosis needs special equipment. The symptoms matched yours perfectly, no cooling, system completely dead, warning light on dash. But turns out the AC compressor was actually fine. The real culprit was a failed AC control unit, which is basically the brain that manages the whole automotive cooling system. Total repair came to 980 Euro including parts and labor. The shop had to order the control unit and reprogram it to work with the car. They also performed a full system diagnostic and refrigerant recharge after the repair. Before suggesting specific fixes though, could you share: Current mileage on your S7, Any unusual sounds before the system died, Whether the blower motor still works, If you notice any refrigerant leaks under the car, Complete error codes from the scan This info would help determine if you are facing the same air conditioning control unit failure or potentially something else.

My S7 has 123007 KM on the clock with the last major service completed at 120000 KM. The blower motor still works fine and I have not noticed any refrigerant leak under the car. No unusual sounds before the system failed. Just went from working normally to completely dead during a regular drive. The error codes from my scan tool show P0645 (AC Clutch Control Circuit) and P0530 (AC Pressure Sensor Circuit). Thanks for sharing your experience with the control unit failure. The symptoms do sound very similar. Hoping I can get this auto AC repair handled under warranty since the car is still relatively new with moderate mileage.

Based on those error codes and symptoms, I am even more convinced you are dealing with the same air conditioning control unit failure I experienced. The P0645 specifically points to the control circuit, which matches my case exactly. The AC unit issues you describe match the classic pattern, sudden failure during normal operation with no warning signs. These control modules have a known weakness in the circuit board that causes them to fail without warning. In my case, the shop first suspected the compressor too, but diagnostic testing of the automotive cooling system revealed the control unit was not sending proper signals to engage the compressor clutch, exactly what your P0645 code indicates. Key evidence supporting control unit failure vs compressor: System died suddenly with no prior symptoms, Blower still works normally, No refrigerant leaks present, Error codes relate to electrical control rather than mechanical issues The repair process should be similar to what I went through: Control unit replacement: ~600 Euro, System diagnosis and programming: ~200 Euro, Refrigerant service: ~180 Euro Make sure to have them verify proper compressor operation once the new control unit is installed. In rare cases, both components can fail together.

Thanks for the detailed information about the control unit. I will schedule an appointment and have them diagnose the system focusing on the AC control module first, since the symptoms and error codes match your experience so closely. Will update once I know if the vehicle HVAC system needs just the control unit or if the AC compressor also requires replacement. Really hoping to avoid any major air conditioning repair costs since the car should still be under warranty. The error codes matching your situation gives me more confidence about the likely cause. Having this information helps when discussing the repair with the service department, especially the P0645 code pointing to control circuit issues rather than mechanical problems with the compressor itself. I appreciate the breakdown of typical repair costs as well. At least I know what to expect if it somehow falls outside warranty coverage.