I hear a hissing coming from dash. It always hissed but everything used to work. The a/c blows cold air and the heat blows hot. Just recently the air only comes out of the defrost vents no matter what setting i put the switch on. Heat, vent, norm, all comes out of the defrost vents except for the the max cold setting that still comes out the main vents. Im curious if the entire a/c /heat deck has to be changed or if it is something else? Also i have noticed that when i put a strain on the motor the hissing goes away. Basically i would like that hissing to stop and the switch settings to work correctly so if anybody can explain why this is happening it would be greatly appreciated ..Sorry for the length of this post

 

sounds like a vacuum line to the heaterbox is disconnected

 

Yep, sounds like a vacuum leak.

 

yes, vacuum line is off or broken somewhere, or it could be the entire control peice. defrost is the default, no vacuum position.

 

what they said

 

im not sure if its been metioned, but i think its a vacuum leak.

 

you know? i think he might have a vacuum leak. nobody ever thinks of something that small

 

Have you checked the vacume lines?

 

It could also be one of the suck hoses that's connected to the heater controls. They're driven by vacuum!!!

 

so i did some tinkering and it turns out...it was a vacuum line. well done everybody