A/C blowing out of the defroster vent

[Sixt8Chrgr]

When I turn my A/C on it predominately blows out of the defroster vent instead of the A/C vents in the dash. I realize there is a door that is open or not closed. Is this an easy fix or not worth trying to fix because of having to remove the entire a/c system. Any advice on how to fix this would be greatly appreciated.

BTW...this A/C system is on a 68 Charger with a 383 auto with console and power steering,power brakes.

Thanks,

[y3chargerrt]

Maybe a problem with the vacuum switch. First make sure you have it hooked up to vacuum.

[Sixt8Chrgr]

where is this switch and how do I do the test?