[psycho bob]

so it's been a bit cold lately and i have no heat coming out of the floor vents nor will air come out of the "face" vents. the only thing that works is the vents when the a/c is on and every other setting comes out of the defrost. i'm sure this is a pretty common issue. so anyone with the fix???

 

[mxnate116]

are all your vacuum lines connected under the dash?

 

[psycho bob]

i could double check, but i bought it from the original owner and they haven't done anything to it. totally stock

 

[nolife]

See this thread. It is not very detailed but should get you started, the flapper is vacuum operated and supplied from the vac tree on the firewall. Follow it from there to the flapper under the dash and to the control knob in the dash. Most issues seem to be a cracked hard plastic vac line in the engine compartment.
http://www.moddedmustangs.com/forums/5-0-mustangs/132203-fans-dont-work-correctly.html

 

[83 5.0]

Some diagrams here that may help in your troubleshooting Mustang FAQ - Engine Information

 

[tmoss]

try this.....

 

[psycho bob]

so started looking yesterday and found a Y with only the two lines that go back under the dash connected. the one that looks like it goes into the engine compartment has no tube on it at all.

 

[tmoss]

might be your problem.......