Why has my vehicle’s heat stopped working?

John Paul, AAA Northeast's Car Doctor, answers a question from a reader who isn't cool with his unheated Jeep Grand Cherokee.

The Jeep logo.
The Jeep logo. –The Associated Press

Q. I have a 2010 Jeep Grand Cherokee. It has been a pretty good vehicle that I keep it for winter travel and trips to the beach in the summer. I have a new Honda Accord for long-distance trips. My problem is that the heat suddenly stopped working. The heater was blowing cold air and wouldn’t heat up at all. I swapped cars and drove the new Honda, and the next time I used the Jeep, I experienced the same problem. I took it to my local mechanic who checked everything but didn’t find anything mechanically wrong with it. Strangely, when I headed back home that day, the heat worked great. I have a couple of ski trips planned and I fear that the heat may disappear again. The mechanic suggested that I bring it to a Jeep specialist since it must be an electrical issue. Do you agree?

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A. The heater valve is a quick check, and it can easily be determined whether the valve works or not. The blend-door control is a little trickier to check. It’s possible the blend door was simply stuck, and the bang of closing the hood allowed it to move and work. Try cycling the heat on and off and see if it goes from hot to cold. If it seems to operate normally, go skiing. If the heat stops working, at least you will be dressed for the cold.

John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE certified master technician. Email your car question to jpaul@aaanortheast.com.