How Car AC Works
With summer upon us, millions of drivers are turning on their car's air conditioner (AC) to stay cool and comfortable. Automotive AC units work just like residential AC units: They use refrigerant to transport heat out of the air, thereby creating cool air that's pumped into your car's cabin. But like all components used in modern-day cars, AC units are susceptible to failure. If your car's AC is blowing warm air, the problem might be attributed to the following.
Typically found at the front of the vehicle -- around the radiator -- the condenser in your car's AC unit is responsible for converting refrigerant gas to liquid form. It contains fins through which the refrigerant flows. As refrigerant flows through the condenser, a fan blows air over it, thereby releasing the heat and turning it to liquid form. If the condenser is clogged, however, it won't perform this conversion. As a result, you may experience warm air blowing from your car's air vents.
Perhaps the most common reason that car AC units blow warm air is low refrigerant levels. Like residential AC units, car AC units contain refrigerant in a closed system that removes heat. Normally, refrigerant levels remain stable, as there's no way for it to escape the closed system. But failure of the condenser or lines may allow refrigerant to leak from the system. When this occurs, your car AC's unit will no longer be able to produce cool air.
Keep in mind that refilling your car's AC unit with refrigerant is only a temporary solution. Unless you find and fix the leak, the new refrigerant will leak back out.
Faulty Condenser Fan
A condenser works in conjunction with a fan to cool down refrigerant and convert it to liquid form. The actual condenser holds the refrigerant, while the fan blows air across the condenser. If your car's condenser fan is broken or otherwise not functioning properly, you may experience AC problems like warm air. Of course, another tell-tale sign of a faulty condenser fan is overheating when idling. The lack of airflow around the condenser and radiator allows heat to build up inside your car's cooling system, which may cause the engine to overheat when idling.
If you're still unable to fix your car's AC, consider taking it to an automotive mechanic for a professional diagnosis. In the meantime, leave your windows slightly cracked after you park and exit your vehicle so that fresh air will replace the hot, stale air inside your vehicle.