So I found a link which I included in this post and it gives a great view and description of what is going on with the Selectaire system.
I does mention the operation of the heater control valve
3. Electrical and vacuum functions are illustrated here. When you apply heat, you are moving the Bowden cable, which affects the heat control door and hot water valve function. The hot water valve is either on or off depending upon vacuum application. Each vacuum port at the vacuum regulator directs vacuum to the appropriate servo motor depending upon control position.
http://www.mustangandfords.com/how-to/interior-electrical/1601-troubleshooting-classic-mustang-climate-controlCan’t road test today as it is bad and stormy weather in Melbourne so I’ve done just run it in my garage.
What I found so far is the vacuum is operating fine as it changes direction of air flow from screen to face to floor so the doors are operating.
However I found that in the off position on the 1 lever and with the cool setting on the centre lever of the control which runs the Bowden cable the fan running in all 3 speeds blows air into the floor area just like when it is in the heat position.
So I’m thinking that either the door doesn't fully close or the foam is deteriorated. The amount of air passing through is the same so I don’t think it deteriorated foam with a closed door as the closed door should still reduce the air flow even if it allows some through.
The door actuator is moving all the way in and out when operating the Bowden cable to and from the heat position so its moving the door from open to closed, but is it closing all the way.
So I’m wondering if there is any adjustment that can be made to close the door totally shut without having to pull out the box.
Just another note....the centre lever doesn't sit in the up position (cool) when i let go of it as it springs down a little, but it will sit in the down (heat)