On my '92 Laredo 4.0 HO, when climbing even a slight rise, the A/C will momentarily blow through the defrost vents until engine vaccum comes back on level ground.

I was wondering if anyone knows which vaccum line(s) control the blend door in the A/C case. I'm sure I have one leaking somewhere but haven't located it yet.

It is getting worse over time. The cruise control does not drop out when this happens.

It also happens when the engine is first started if the A/C is already on until vaccum builds.

 

Had the samething happen to me so i went ahead and went down to the dealership and got the whole vaccum line and resivor for like $40. Might be cheaper. Anyways the line comes out of the mainifold back to the firewall and over to the winsheild wiper fluid, then comes to the front of the compartment and down in to the front bumper hope that helps. Easy way to do it is find the resivor and follow it back to the mainifold. the resivor is located in the passenger side front bumper. good luck on that leak.

 

The reservoir might have a crack in it. I will check that first tomorrow then work my way back towards the firewall.

 

definately sounds like a vaccuum leak. let us know what you find.