If you can't get your vehicle's AC system to work, driving when it's hot outside can be a nightmare. Instead of torturing yourself, use these repair tips to your advantage. Have a Professional AC Performance Test Performed Since there are many reasons why your vehicle's AC system may not work right, the best thing you can do is take your vehicle in for a professional AC performance test. Auto repair technicians will run an extensive test that check's your AC system's coolant levels, coolant lines, seals, compressor, and condenser.