Dealing with a 1986 Olds Cutlass. I need the break down on how the vent control system works, problem I`m having is the heater vent stays open, so when your going down the road there`s air coming out of it and it gets hot or cold depending on where the thermostat slide is set at, so I removed the controls out of the dash and checked it out, no matter where the selector is set, the vent never closes, If I remember correctly it`s suppose to close when it`s set to off and everywhere else except for heater, I checked the vacuum canister that controls it and it`s good, it holds vacuum, it`s just never getting any vacuum. The next thing is the vacuum lines go to the selector, but there are 2 more vacuum lines that run off those to 2 posts on the right side of the selector, you can hear the vacuum leaking, and it leaks continuous no matter where the selector is set, the only time it doesn`t leak vacuum is when it`s set to Max A/C. I`ve heard these leak before on other GM cars when you set them to off, but they would soon stop after a minute, these continue to leak, going down the road you hear the constant hissing sound. Anyways, if anyone can give any help on how this thing works so I can get it all back in the correct working order would be much appreciated.