Vacuum - Dash A/C Routing Issue

[deafmetal]

I swapped a L67 3800 into my Lumina years ago. One thing I never figured out was why I lose A/C routing inside the dash when I mash the gas.

All the air routing and controls in the dash are vacuum module controlled. I ran a hose from the vacuum header on the front of the Supercharger vacuum header to the dash. At idle and normal acceleration, the dash vents properly, it is getting the proper vacuum. But when I mash the gas, I'm assuming the boost from the supercharger is causing a loss in vacuum on that line, and the modules controlling the vent air routing revert to defrost position. I let off the gas, vacuum settles out, and the modules re-route the air back to the proper vents.

Obviously this sucks during 110 degree heat going up a hill when the A/C gets re-routed to the window defrost position...

Am I missing a check valve or something somewhere? I have the vacuum tank attached. Keep in mind this is a 97 Grand Prix L67 and the 1991 Lumina dash controls. Does the 97 Grand Prix use vacuum controlled vent routing modules in the dash or newer electrical modules?

Appreciate any thoughts, suggestions or ideas.

~Rob

https://www.deafmetal.net/Auto/

[CNCguy]

Put a check valve between the vacuum tank and engine. That should take care of it.

[deafmetal]

Thanks, will try.