1987 Chevy Silverado V10 A/C mode/selector door not working properly.

[SBarbara]

 Working on a/c-heater box under dash to try to detect why air won't blow from dash vents but only from floor and defrost. Long story short after fixing vacuum leaks and so on, I finally got mode/selector door to open when selecting max. cool and normal settings. The door will only open 1 1/4".  My vacuum is 17-22 inches which is normal and has no leaks . Did smoke test when fixing leaks to verify. Now the vacuum actuator that controls the door is mounted on the backside of the ac-heater box which is against the fire wall. I sure don't want to take the ac-heater box out and replace the actuator if that's not the cause. I would think the door should open all the way . I would really appreciate any help someone will give me on this .
Thank You
Scott
     

[75gmck25]

There are two actuators in/on the box at that location, but you can only feel/see the one up against the firewall on the back.  There is another one inside the box, and on my truck there is a small hose and nipple sticking out on top, which is where you connect vacuum to that other actuator. 

Somehow these  two actuators work together, because one is called A/C mode and the other is called Heat mode. My truck has a partially open position on that door, and then a completely closed and comepletely open position.  If the system is off or on Bilevel the door is about 1/2 open, and in defrost mode its completely closed.

There is also another actuator on the left end of the box near the driver's foot.  This moves a door/flap up and down to close off flow to the heater vent that is right in the middle. You might want to verify that the door is completely closing when in the A/C or vent mode.

Bruce