i have a 91 mustang 2.3 and the heater controls for where the air comes out doesn't work right. when it is set to off, it's off, but any other setting it will come out the dash/defrost. vent will come out the dash/defrost, same with floor and so on. does anyone know why this is??

 

This is generaly caused by a vacuum leak to the asessories. There should be a vac line off the manifold going either into the firewall or to a vacuum reserve canister and then to the fire wall. Find that line. There is also usualy a check valve on that line that could be faulty

 

Prolly not a check valve. There is however a vaccum line going from the manifold going through the firewall, they have a tendency to break, crack. Then it throws all the air to defrost. Just my 2 cents.

 

alright, thanks a lot everyone, i'll try those and let you know if it works or not. thanks again

 

definitely a vacuum line problem somewhere either in the main tube coming into the the passenger compartment over near where the heater hoses go to the heater box or in the control switch itself on the back side where the tubes plug into it or leave it going to the various damper controls.