I have a 1989 Ford Mustang 4 cylinder non turbo.My A/C will only come through the defrost vents.I have done a lot of reading and come to the conclusion that it is a vacuum leak but I have no idea where to look.I would appreciate it if someone could point me in the right direction thanks.

 

Hi,

Do the any of the vents work at all when you switch positions? If not then you have a damaged vacuum hose somewhere.

The vents work with the help of engine vacuum to change the actions of the blend doors. When they loose there functions to change positions, it goes into a safe mode of just the deforst mode. The reason for this is per se winter driving. You need that hot air blowing onto your windshield so yo can see

If i were you, id trace all the vacuum lines going into the firewall from the engine bay and trace them back and look for any type of damage. There is a vacuum ball located in the passender fender area. To access it, you would need to remove that spalsh shield. You could also pop off the trim peice that covers the bolts needed to remove the HVAC controls, remove the and check the vacuum lines there and so forth.

Hope this helps somewhat