When the AC is first turned on it blows very cold, then after a while it starts to blw hot air.
Air blows hot after awhile. on 2009 Nissan Altima
if you go out three days in a row and each day the a/c starts out really cold but gets slowly warmer ..say after about 20 minutes then your not low on refrigerant (unless theres a ghost re-filling it at night) The next time you have a chance , open the hood , find the a/c compressor ,make sure you can see the compressor clutch(belt goes around it)at the end.Thenturnthe key to 'on' not run and turn your a/c ,defrost controls to 'off'.Now have someone start the car while you carefully observe the a/c clutch. With a/c turned off , belt pulley should be spinning (yeah-duh) but the clutch should not be.Assuming it's not engaged now , go ahead and get your helper to turn on the a/c (on vent setting with fan on high and windows down)turn temp to coolest. Watch the fan clutch(caution may get boring for a minute or three.................THEN BAMM........okay not really , leave everything the same except turn the fan speed to low and continue watching the fan clutch and listening.By now ,if it hasn't already , it should have cycled on and off or it should start cycling soon two -three minutes max.IF compressor isn't cycling NOW you need to bring it to a trusted place for diagnosis of the control system. OR if it' hard to find a shop you trust the dealer can usually be the easiest to hold accountable for their diagnosis and repair even though they may be pricier initially. good luck
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POSS FREON LEVEL ISSUE HAVE IT CK'D BY AN A/C MECH TO DETERMINE IF CHARGE IS NEEDED OR SOMETHING ELSE IS WRONG