[header] How to diagnose a non working air conditioning in a car [title] Turn the air conditioning on while the car is running. [step] The air conditioner won't run properly unless your engine is running. The best setting for diagnosis is " fresh air " (not recirculated) with the air blowing out of the center vents in the dash and the ac turned on. 
[substeps] Start with the fan speed turned to its highest setting. If your car has a " max ac " setting, select that option.