the other day i noticed a hissing noise coming from behing my HVAC controls in the truck. Now no matter what setting i put it on, air comes out of all the vents. When i stop moving the air gets cold and when i start driving again it gets warm. its strange. any ideas?

 

The hissing thing is most likely a leaking rotary vacuum valve. Start the engine and close all doors/windows and put your ear next to the mode switch...if the hissing is coming from here you need a new valve. Some of them are available seperate from the entire HVAC control head, and some of them aren't (you have to replace the entire thing sometimes) but it's hit-or-miss. As for the temp thing, that sounds like you are low on engine coolant, it should have nothing to do with the vacuum leak, because the temp valve actuator (moves the temp door from hot to cold ) is electric not vacuum controlled.

 

is it possible that the vacume line could of popped off?? i gotta check it out this weekend

 

Anything is possible but I tend to think lastcoupe has it with the rotary valve. There should be a cluster of vacuum hoses at the valve but it's usually the valve itself that fails.