Vacuum Vents

[rburro2]

I recently switched from the vacuum hubs to manual hubs. Now my vents switch to defrost anytime over 2500rpm. I know the vents are vacuum actuated. Was I suppose to do something to the vacuum lines at the hubs when I installed the manual ones?

 

[RonD]

Just plug the vacuum hoses with screw or bolt of the right size.
Or track down the hoses and remove them and plug the source.

The climate control vents are vacuum activated, and that vacuum comes from a Vacuum reservoir in the engine bay, looks like a black plastic ball, passenger side front down low, sometimes under the frame rail.

Same symptom can occur when this reservoir is cracked.
When you accelerate vacuum in the intake manifold drops down, the reservoir keeps vacuum to the climate control high via its check valve, same as power brake booster uses to keep high vacuum at higher engine RPMs.

If PVH system was sharing reservoir then it being "open" now could account for the lower vacuum at climate control while accelerating.

Defrost is the system OFF vent setting, so no or low vacuum = defrost vents

 

[rburro2]

Thank you, I will do that as soon s my son decides to stay home long enough with the truck so I can.