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2003, 4 cyl. Elantra with 105k miles. Recently after noticing the temp of the air coming out of the AC vents seemingly changing, I placed a thermometer in them to measure the temperature. The theremometer read 39 degrees when the air was blowing cold and up to 59 degrees when the car began to warm up. The compressor is not switching off to my knowledge but I am worried about it becoming a bigger problem if I dont fix whatever is broken soon. This temp change happens about every 10 minutes and the cold air comes back in about 45 seconds. Any help?? I live in FL so figure high 80s/low 90s outside temp and happens whenever the engine is running...regardless whether Im driving it or not.

If coolant (134a) quantity is marginal, your compressor would start to engage and disengage by itself and blows cool and warm air, respectively. Since the compressor is not switching on/off by itself, I guess that means you have good coolant quantity. Ideal temperature at the evaporator is 32 deg F. I believe most cars use somthing called thermal expansion valve (TXV) to regulate the temperature by controlling the refrigerant flow to the evaporator. You may want have the shop checked out the condition of the TXV. Good luck.

wajangchang