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86 Comanche heater problem

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Hey guys, i'm having a problem with my heater. The only thing place that it will blow heat from is the defogger option. No matter what the control setting, it blows by the windshield. It just recently starting doing this, can anyone point me in the right direction?? Thanks guys!

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Yep -- you have a vacuum leak. The heater controls use vacuum to control the flappers, and the default position when they lose vacuum is the defrost position.


On an '86 I don't think you have the round or oblong vacuum ball or "blimp" that the later models have, located behind the front bumper on the right side. I believe yours should have the tin can vacuum reservoirs -- look under the hood, on the right side of the vehicle, probably mounted on the inner wheel housing. Follow all the vacuum tubing and look for cracks and/or splits.

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i think 89 was the change over between the ellipsoid and the sphere, my old 89 had the ellipsoid, my new to me 89 has the sphere

No, my '88 has the sphere.


The sphere has only one chamber, the ovoid has two chambers. It was used with some extra options, usually cruise control (which uses engine vacuum to regulate the speed).

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