Hissing behind dash and no air

[stuartr]

On my 08 v6 mounty I have been hearing a hissing noise that sounds like it around the air/heat unit. It seems to be worse when you go into a curve and shift the vehicle a bit. Also with the air running it is like it just quits blowing out of the vents. I have the climate control air or whatever it is called the auto system. I searched around and didn't see anything about the hissing noise. Could it be vac. leak?
Stu

 

[Town]

The Electronic Automatic Temperature Control (EATC) system uses 2 electronic actuators for the driver and passenger blend doors and 4 vacuum motors for the air inlet door, panel door, defrost door and floor door. The EATC controls the vacuum motors using a manifold attached to the back of the EATC unit in the dash.

For auto A/C the EATC will set full vacuum to panel and defrost doors and no vacuum to floor door and air inlet door. This will direct outside air to the panel vents. If the vacuum is weak then the panel door will close and the defrost door will open. Therefore outside air will be directed to the defroster vents.

If that sounds like your problem then you may want to check the manifold behind the EATC unit for cracks or leaks or hoses that are leaking. Also the motors could be leaking. I think the panel motor has the red nipple on the manifold.

Good luck.

 

[stuartr]

THanks Town, it has abotu quit doing it now. If it starts again I will look for leaks. Good info you gave me! Stu