[Hutch]

zyggy72,
On my 71 with factory a/c there is not a spring to return the flap to the open position.
This vent is normaly open with no vacumn applied. When the vacumn auctuator is installed it will hold the door open at its rest (no vacumn applied) . When vacumn is applied the door will shut.
Inside the cowl area there is no return spring attached to return the vent to the open position.
The only spring inside the cowl is the one around the pin which points to the inside of the cab. This is sping loaded pin which enables you to install and remove the flap within the cowl.
It kinda looks like a sping you would see inside a ball point pen.
Here is a pic of the actuator at rest with no vacumn applied: