First post here, but I have to start somewhere. I bought a really clean 85 gt last week and i'm now going through it. I've found the heater only blows through the defroster. I had the dash apart last night and discovered that this appears to be vacuum operated. I noticed a small vacuum canister behind the glove box, but it couldn't possibly be big enough to run this system. Does anyone know where the main vacuum tank is? Or have any tips on what could be wrong with it?

 

these may help ...
https://mustangforums.com/m_563238/tm.htm
http://www.veryuseful.com/mustang/te...uumDiagram.jpg

I'm pretty sure thats were it is but I'm not positive... did u run self tests or codes...

Are the dash vents open? J/K

 

Thanks. That's a big help. Hopefully just somethings disconnected under the hood. The cruise control doesn't work either, so i'm hoping it's something related.