[455-4+1]

I went through 10 pages of search results but couldn't find the answer ?

I have the body manual but couldn't find it in there either .
2x Queries as follows

Query #1
Under the hood, passenger side near the firewall, there is a vac diaphragm which operates a door / gate. Mine has red stripe vac tube going to it which looks correct. The diaphragm was buggered so managed to get one sent from Franks to New Zealand along with a few other small parts, don't ask me how much !!!!

The diaphragm was a direct replacement for what was on there and seems to work great. Its one direction, (pull only) which seems correct (I think, and hope so !!!)
If that's the case, what acts on the door / gate in the other direction ?
Possibly there is a light spring that is broken somewhere (hopefully not down in the bowels of the heater system !!!).

I manually tested (suck !) the Defrost one under the dash, (yellow tube) and it pulls with vac source, then returns with vac released. Its a single action diaphragm like the other one.

Query #2
The diagrams in the manual show a vac check valve under the hood on the feed line. Mine doesn't appear to have one (a lot of the heater stuff was non functioning as car sat for a long time). Is this a special valve or something - or just a one way check valve (I have a few of them). If so install with vac able to pull from intake, but not release when engine turned off, assume this should be full manifold vac, not ported ?

Here's hoping there isn't a spring missing on the air valve door, or its a simple one to get at !!!

Thanks in advance