Questions and Answers

Jimmy Heater Problem Q. I have a 1998 GMC Jimmy SLE 4.3 V-6. When I turn the heater on in the Jimmy it comes out of the defroster, it does not come out from the floor. When I set the dial for defrosters it works fine. When I set the dial for the vents it works fine. But when I set the dial for the floor it comes out of the defroster. What could be wrong? Thanks for your help.

A. The air distribution system in your truck is vacuum operated. The most common problem is either the vacuum motor at the air door is bad, the door itself is jammed or the vacuum switch in the control panel.

The check it you have to get under the dash and see if vacuum is going to the vacuum motor. If it is then the motor is bad or the door is jammed. If you can move the door by hand, then it's the motor. If you aren't getting vacuum to the motor then the vacuum switch in the control panel is bad and needs to be replaced.

Additional Information provided courtesy of ALLDATA