2001 quad cab sport 4x4 5.9. When i get on the gas or even just climb a hill on cruise the blend door moves from the vents to the defrost then back again when the engine is no longer under a load. Thinking a vacuum problem. Any ideas?

thanks for the help

 

A common problem. Do a search for "wild vents", lots of info.

 

Yup, vacuum problemo. Good start for searching what Arde said.

Follow all vac lines and check them. You may have one cracked / broke / etc. After ruling that out, then you might have blend door issue. If the the bushing has broke-dead, then replacement is Heater Treater (google-fu it).

 

It was a vacuum leak, as you suspect in your case. I don't remember exactly where the broken line was, as I paid a shop to repair it, but I would start by tracing the vacuum lines back from where they connect to the passenger side of the intake manifold.

Good luck!

 

Use a vacuum pump and check lines to see if they hold vacuum. If all looks good verify the two check valves on the passenger side of the motor are functioning properly. Take them off and blow through both sides, they should flow one direction only. I just fixed the same issue this morning on mine and used a Dorman 47149 valve which cost $7 at the local parts store. The diaphragm was screwed up on the one near the intake manifold for me and flowed both ways. With this new one I had to make up a reducer on one side to adapt to the stock T-fitting. Took all of 5 minutes and some spare hose / a reducer fitting I had in the parts bins