The automobile air conditioning system in a car uses a coolant, stored in a radiator, to remove heat from the air moving over the engine. This "cooled" air is blown over the engine, into the evaporator, then blown into the car. Foul smells and hot air coming into the car can indicate an issue with the AC. Although a car air conditioner is built differently between models, you can take some basic troubleshooting steps to diagnose your problem.
Turn on the car. Check that the AC switch is turned to the "On" position. Allow the car to heat up, and check the air to see if it is cold.
Flip the AC switches along the different functions. Turn the knob, and feel for loose points. The control panel may need to be changed if the knob is loose.
Turn off the engine, and allow the car to sit for about an hour to cool the engine.
Place a rag over the radiator cap. The radiator is at the front of the car, and the cap is on top. Turn the cap counterclockwise to release it. Check the level of radiator fluid inside. Add mixed coolant (half coolant, half water) in the radiator until it is full, and add mixed coolant in the reservoir until it is at the "Cold" level.
Inspect underneath the car for any cooling leaks. Refrigerant from the radiator will appear neon yellow, orange or pink. Follow the lines from the radiator back to the evaporator, squeezing the lines along the way. Any plastic line that feels hard or is cracked should be replaced.
Smell for any unusual odors when the fan is turned on. This means the evaporator needs cleaning.
