Heat and Air trouble

[SchneiderFishing]

Every time I accelerate, even just a little, the heat or the air stops blowing from the dash and only blows through the window defrost vents in the top of the dash by the front windshield. Any ideas? 1990 Comanche 4.0 Column shift 4 wd

[aemsee]

You have a loss of vacuum to the heater control head. Defrost is the default position for safety. Follow the vacuum lines from the engine to the firewall and down to the vacuum canister.

[Pete M]

Yup. Sounds like a vacuum issue. The most common failure points in the system seems to be the vacuum lines as they enter the vacuum canister (which is located inside the front bumper on the passenger side). :thumbsup: