Well my ram is showing its age a lot of problems arising. This one is about vacuum. I have the wild vents. I check for leaks there are none. I check the check valves they are good. But I still have the vents go to the defrost position when vacuum drops. Please help.​

 

Add another vacuum reservoir under the cowl grating. (and verify that the one that is there isn't cracked.

 

The valves need to be replaced if they are over 3 years old. They may appear good, but they wear out. I replace mine every 3 years or so. Both acted perfectly when "checked" but I had wild vents for the umpteenth time. Just replace them. AC Delco parts on Amazon are the perfect match and OEM.

 

What year truck? There was a tsb on adding a check valve depending on year.
https://dodgeforum.com/forum/2nd-gen...fan-speed.html

 

Forgot to mention it has that check valve. It a 01 with 96 dash and wiring