My latest purchase of a T/A definatly constitutes as a project car, and one of the issues I have no clue about it is the HVAC.

It only works on Defrost mode, (but both cold and heat can come in depending on temp slider thing), and when anything but the coldest setting is on,(so any form of heat) it hisses when throttle is applied, and only when throttle is applied...

Can anyone tell me if this is a wiring issue in the HVAC controls or should I be posting in a different category?

 

Sounds like there is a vaccuum line off somewhere causing the controls no to work properly.. I would check that first.

 

To check your vacuum, there is a vacuum ball that takes engine vacuum and then goes to a hard plastic line along the firewall, which feeds your A/C controls. This diverts the doors to move air to the different vents. Check the connection at the back of the control and make sure all the vacuum lines are secure. Same thing for the engine vacuum line.