Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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.

share|improve this question

Does your car overheat too?

If so, you could have a faulty thermostat, an air pocket in your cooling system or maybe even a leak somewhere. My truck's heat would only work while I was driving, then stopped working altogether while the engine started to overheat. I changed the thermostat, then the heat would blow hot/cold/hot/cold, I didn't realize you had to bleed the air out of the system after changing the thermostat. I did that and now the heater and engine run great.

share|improve this answer

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.

share|improve this answer
All the cars I'm familiar with leave the heat alone when the A/C is switched on since conditioned, warm air is sometimes required (example: defogging windshield). – Brian Knoblauch Nov 21 '13 at 19:21
I suspect newer vehicles with thermostat-based climate control systems may shut off the heat when the AC is on, except of course in defrost mode. So this answer seems at least plausible. – R.. Nov 22 '13 at 0:02

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.