Blowing on defroster while accelerating

[Digitalgp]

I’m having an intermittent issue where sometimes when I accelerate the Hvac system changes to the defroster vents, but when i get off the gas it will return to the dash vents.

Would this be an issue with the vacuum canister or just the check valve? Also are these located in engine bay or behind the dash?

 

[Rcflyer330]

Its the check valve. Its located on the passenger side in the engine compartment and its a small diameter grey or black line with the valve in the middle.

 

[Digitalgp]

Thanks for the help!

 

[gtyates]

Just saw this post. Yep, check valve. Cheap and easy repair.