On a hot July day, the key piece of equipment is the auto air conditioning compressor. This is the device that not only circulates the cold air from your air conditioner to your car’s interior, but it also removes the heat from the air conditioning system. Indications that the compressor could be failing include, a non-turning serpentine belt, or a belt that has a huge wear patch in it. To test your air compressor, try turning it by hand. Even though the engine is off, it should still turn, albeit with lots of resistance. If it doesn’t turn at all, it indicates that the clutch and compressor are broken and must be replaced. Full service will cost about $500.
For more info, see Auto AC Repair Tips