This started about a week ago. I put the heat on and about after driving a couple of miles with the heat on it would randomly blow out cold air. Sometimes if I turned the heat off or switched it from cold back to hot it would work again. How would I go about fixing this or even knowing what the cause of the problem is? Also, this is the first time this has ever happened to me and I have owned the car for a little over 4 years now. 2001 Nissan Altima.
First check would be that the engine has sufficient coolant. (NB Do not remove the radiator cap when hot). Second check is that the engine is reaching operating temperature - does the temp gauage rise and show hot?. If these items pass inspection, then the very probable fault is with the AirCon module. When you turn the AirCon on, the module shuts off the flow of water to the heater. When you turn the AirCon off, the module opens the flow of water to the heater. A mis-behaving module would give you the heater performance you are experiencing. A system scan of the AirCon should highlight the fault.