I have a green switch on my aux. fan, does the system have to be evacuated to change this to the lower opening pressure red switch i have been hearing about?

I believe my recirc/fresh air door is not working, when I hit the recirc button nothing changes, where is this door located so I can see if it is working?

BigRichard72@home.com

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BigRichard1972

1987 Mercedes 260e (w124)
1968 Chevy Truck "Goldie"
1985 Brunette "Margaret"