A/C defrost problem

[dwithers]

My A/C only blows out the defrost (default). Any ideas on where to check for a loose vacuum hose?

 

[digorok]

Leak in vac

Check to make sure the vacum line in the engine compartment is not cracked and still conected to manifold vacum.
Start the engine turn the blower fan to low and listen to the areas near the vent controls in the center of the dash, or under the passenger dash (open the glove box), you maybe able to hear a hissing sound from the vacum leak. If you have some way to make constant vacum (A/C vacum pump), you can conect it to the vacum line in the engine compartment and not start the engine making it easier to hear.
Most of the time I've found that the plastic vacum line in the engine compartment has become brittle and cracked, or the control head vacum conector has come loose and is leaking, or the control manifold is leaking.
Hope this helps.

 

[first turbo]

SO DOES MINE, AFTER ABOUT 10 MINS. OF RUNNING IT STARTS BLOWING OUT THE DASH VENTS

 

[fitz3820]

The same thing happened to my GN, the control manifold was leaking. It was ~ $17 from my friendly neighborhood GM dealer.

I would chcek the lines under the hood first though.

Mark F.

87 GN 11.9 @ 115

 

[salvageV6]

A/C in MAX position should have vacuum on the purple, blue, yellow, orange, and gray hoses.

Make sure the purple hose has vacuum at all times when idling the car. Source is the vacuum ball under the front fender.

 

[SuperSix]

Check ALL vacuum lines, mine was caused by a vacuum hose that kept popping out of the EGR solenoid.

Also, the temp door sometimes sticks, that's the delay you ee with the vents opening.