To troubleshoot an automotive air conditioner, check the refrigerant quantity, look for refrigerant leakage, and find out if the compressor and its fan are working as required. Also, check if the cooling is intermittent and if there is any malodor coming from the unit.
To check if the coolant is adequate in the automotive air conditioner, determine the pressure using a pressure gauge when the car's engine is switched off. Compare the reading to that given in the owner's manual; if it is very low, add more refrigerant when the car cools. Then, run the engine for several minutes, switch if off, cool, and check the pressure again. If the reading is still low, repeat the process.
To detect refrigerant leaks in the hoses and their connections, spray a solution of soap and water on them. Presence of bubbling indicates coolant leakage. Also, check the condenser, the compressor's O-ring and the radiator fluid levels to detect leaks, and look for signs of coolant leakage on the driveway.
Check for a blown fuse in the compressor, and replace if required. If the clutch of the compressor is functional but does not start the unit, replace the compressor. When the car's air conditioner and engine are switched on, the compressor's fan should start after a few minutes. If this does not happen, it indicates a dysfunctional fan that needs replacement.
Unusual noises from the air conditioner indicate a failing compressor or the hoses hitting other automotive parts. Malodors indicate mold growth in the unit's evaporator. Drain the evaporator's drainage tubes, and use a spray to prevent mold growth.
If the air conditioner cools intermittently, evacuate the air from the unit using a vacuum pump. Also, identify damaged switches, temperature sensor and electrical connections, and have them repaired by a professional.