Heat will only come out of my defrost vents no matter what setting I have it on which should mean that it's in "default mode". Since I have the vaccum control setup I am guessing there is a vaccum leak somewhere. Where is the main vaccum line for the controls located? Has this happened to anyone else? If so what was your problem?
I was also wondering if the A/C delete heater controls are cable or vacuum operated.
Thanks everyone!!

 

Do you hear any hisssing coming from the heater controls?? if so you have to trace where it's leaking.

i don't know where the main vaccum lines go but under the hood on the driver's side is a black box with two lines in them one of them is the vaccum you need to control the settings.

although, i have a 85 z28 i dunno if your year is the same.

 

I had a problem like yours. My main vacuum line to the heater controls got melted by an over heating wire alnog the firewall. The melted vacuum line got sealed so I had no leaks.

My main line on my 86 went from a T near the brake booster, along the firewall to the pass side and then into the car. The line that runs across the firewall is a plastic one.