Audi A4's Dead AC: Compressor Won't Engage

I had a very similar AC efficiency problem with my 2014 A4 1.8T last summer, and I have some experience working on basic car maintenance tasks. The symptoms were identical, no compressor engagement and complete loss of cooling. After checking fuses like you did, I took it to a certified workshop since AC systems require specialized diagnostic equipment and expertise. The main issue turned out to be defective valves in the AC system that were preventing proper pressure regulation. The repair involved: 1. Full system diagnostic test 2. Replacing multiple control valves 3. Evacuating and recharging the system 4. Testing the blower motor and temperature control functionality Total cost was around 1000 Euro including parts and labor. The repair took about 6 hours to complete. After fixing, the AC performance was back to normal with proper cooling. To help diagnose your specific case, could you provide: Any unusual sounds from the compressor area? Does the blower motor work on all speeds? Check engine light status? Current mileage? Any recent AC maintenance history? This information would help determine if you're facing a similar valve issue or something else in the cooling system.

Thanks for sharing your experience. Just had my regular service at 96396 KM and they didnt mention any AC issues back then. To answer your questions: no unusual sounds since the compressor isnt engaging at all, blower motor works fine on all settings, and no check engine light. Based on your case, it sounds like I might be dealing with a refrigerant leak or pressure-related issue in the AC system. Your mention of valve problems is helpful since its similar to my symptoms. Will need to get proper AC diagnostics done to confirm. Were the temperature control readings normal in your case before the valve replacement?

Thanks for those details. Yes, in my case the temperature readings were normal through the climate control display, which made the valve issue less obvious at first. Like your situation, my AC relay and compressor showed no signs of life. After the repair, I learned the AC pressure switch was actually sending incorrect signals, preventing the compressor from engaging. This caused the system to behave exactly as youre describing, no engagement but normal blower operation. The similar mileage and symptoms suggest you might be dealing with either: Failed pressure switch (common issue around 90-100k km), Faulty AC relay, Low refrigerant triggering the pressure safety cutoff Without proper AC diagnostics equipment, its hard to pinpoint the exact cause. My suggestion would be to have a shop perform a pressure test first, as this could reveal if youre losing refrigerant or if the pressure switch is malfunctioning. The good news is if its just the pressure switch or AC relay, the repair cost should be significantly less than what I paid for the valve replacement. A basic AC maintenance check might be worth it before authorizing more extensive repairs.

Thanks for that detailed explanation. Your case definitely sounds similar to mine. After hearing about the pressure switch being a potential culprit, I did some research and found quite a few similar cases with the same AC efficiency problems around this mileage. The fact that your temperature control readings were normal before the repair matches my situation perfectly. Think I need to stop trying to diagnose this myself and get proper AC diagnostics done to check the pressure levels and switch functionality. At least now I have a better idea what to expect and can discuss these specific points with the shop. Will schedule an appointment this week and make sure they check the pressure switch and relay first before looking into more complex cooling system issues. Really hoping its just the switch, definitely prefer that repair bill over a full valve replacement like you had. Will probably start with a basic AC maintenance check as suggested to rule out simpler issues first.