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Discussion Starter · #1 ·
I'm having problems with the vacuum controls on the '99. It acts like there is insufficient vacuum to operate the various doors and controls in the system. For example, if I stop at a light, the blend door will open up and the air will get warm until I step on it a bit and it snaps back and it's good and cold on the AC side again. I also have air coming from the floor heat vents when the switch is on vent.

It sounds, to me like the selector switch is acting up or I've got a bad connection somewhere and it is losing the vacuum. Any suggestions as to where to look first? :crazy:
 

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Since the source of your vacuum is (ultimately) manifold vacuum, which is high at idle, it does not really make sense that this is a vacuum problem. Further, the temperature blend door is controlled by an electric motor called an actuator. So before pursuing the vacuum controls , please consider removing the right interior knee bolster panel, and maybe even the crash brace behind it. This should reveal the interior half of the HVAC. Mounted on the far right is the blend door actuator. By removing the actuator from the HVAC box you can then get a glimpse of what I think is the problem: A broken door shaft.

This is a picture of a 03 Explorer HVAC box that has a broken door. You can see that the actuator (white square thing) shaft will not properly engage the door shaft.

 
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