Why is my car A/C blowing warm air?

Air conditioning does not consume refrigerant the way an engine consumes oil. In a healthy system, the same refrigerant circulates indefinitely.

So if yours is low, it escaped somewhere. Adding more without addressing that means the leak keeps going, and there is a second cost: refrigerant carries the oil that lubricates the compressor, so running low is hard on the most expensive part of the system.

How your A/C fails is diagnostic information, and it is worth paying attention to before you call.

Not every A/C complaint is refrigerant. A cabin air filter clogged with debris will make even a perfectly functioning system feel weak, and it is an inexpensive part.

Cooling fans matter too. At highway speed, air moves through the condenser on its own. In traffic it depends entirely on the fans, which is why a failed fan produces A/C that works when you are moving and quits when you stop.

Leaks are found by looking for the oily residue refrigerant leaves behind, by adding a UV dye and checking with a black light, or with an electronic detector.

Common leak points are the condenser at the front of the car where road debris hits it, rubber hoses that harden with age, O-ring seals at connections, and the compressor shaft seal. Once the leak is repaired, the system is evacuated and recharged to the exact specified capacity — a system overfilled with refrigerant cools worse, not better.