Hi everyone im having a problem with the climate controls. The a/c will not come through the vents only on the floor I was wondering where I should start lookin to solve the problem? Let me know thanks

 

You are not alone my 89 mark cross did the same thing. behind passenger kick panel underneath glove box there is an access panel to the plenum assembly in side that black box is the controller for the plenum doors, problem is that one of 2 things went bad.
1 diode , 2 capacitor on that small panel. its easy to trace it has seven vacuum hoses and a 5 wire connector to it.