Does the engine actually overheat or just run hotter than normal? The engine overheating won't have anything to do with the A/C blowing warm air, but the A/C running will ALWAYS make the engine run slightly hotter than normal. This happens because when you turn the A/C on, it places a load on the engine than produces more heat the cooling system has to deal with.
Also, have you inspected the drive belt? If it's worn, when you turn on the A/C it stretches slightly. If it's too worn, it'll slip and the water pump won't turn as fast as it should. And a excessively worn A/C compressor is harder for the engine to turn than a good one.
When the radiator was changed, was the system flushed? Also, inspect the lower radiator hose for softness, as sometimes the hose will collapse and block the flow of coolant.
Tuesday, February 1st, 2011 AT 12:15 PM