So now that it is spring and I want to get vent air and the a/c out the panel vents I noticed a problem. Intermittently for anywhere from 45 seconds to 15 minutes my truck will only route air through the defroster vents. The air varies temp with the switch and fan speed but it will just stop blowing out the panel and blow out the defroster for awhile. Nothing I have tried as far as flipping the switch around has helped. I have seen some other posts like this when I did a search and a guy who had the same problem said it was not his control panel. Does anyone else have anything I should check? How are the gate systems operated? Is it a vac line that might have a crack in it?

Any experience or ideas are appreciated.

 

sounds like a vac line to me what is this on..

 

there is a small plastic vac line in the engine bay of your truck, near the heater core. that line is probably broken. Mine did that all winter, finally figured it out about a month ago.

 

gotta b a vac line

 

Sorry about that. It is on a 99 Dakota, CC, Sport, 318, AT, 4x4

 

try what mhicks said, that would be my guess too, if not then ya get to start checking stuff in the dash its a blast!