Jeep Wrangler Heater Problem



I have a 1997 Jeep Wrangler TJ and I love it! The problem I do have is that when I’m driving and reach a speed of 50 mph or more the heat or a/c starts blowing from the windshield defrost location no matter where I have it set to come from (i.e. the floor or dashboard vents). I had it checked out and the mechanic said that the vacuum tubes weren’t leaking air, and that the system might just not have enough vacuum pressure to overcome the air passing through the grill and I should add a reserve vacuum tank. It seems like that would have been done as OEM if that were the case. Any thoughts?


If vacuum is lost to the ventilation system in your vehicle, it will automatically default to the defrost mode. Did they check the vacuum reserve canister for the vent system located behind the right side of the front bumper?



I doubt it, I’ll have them check that a.s.a.p. and if that’s the problem then I thank you very much!


The lines on newer cars are very small. They’re intolerant of leaks. Normally I would expect your system to cycle all the time in and out since you’re changing the manifold vacuum quite often while driving around on surface streets. The leak must be small since it doesn’t exhaust the vacuum reserve except at highway speeds.


That makes a lot of sense, because it isn’t a problem at all until I get up around or over about 50 mph. I suspect that the mech. I took it to didn’t spend a lot of time checking for leaks either. It is such a pain because it is a cold enough vehicle in winter (in Michigan) with the soft top and when that heat isn’t blowing directly on you… Then, during the summer if the weather is iffy and I have the top on the a/c fogs up the glass.