There is a vacumm hose under the hood going from front passenger diagonally across the engine to the driver rear side. Most likely it is cracked or broken completely. Tug lightly on the tubes to verify if broken, slip an over jacket bit of tubing temporarily, replace whenever, you will have to open the inside engine cowling to get to the rear hose terminal.
Hey my father in-law had the same issue. I made this video to show the hose mentioned above.
cheers
Nick
http://www.truezombielife.com/ventilation-issues-safari-astro-mini-van/
The vacuum switches for the AC vents on a 1995 GMC Safari all-wheel drive van are located underneath the dashboard. The vacuum lines are also located underneath the dashboard.
The AC does not blow on the main front vents. Only rear and defrost.
You have a broken vacuum hose under the hood that supplies the switch.
GMC safari has twoconverters
why dont bottom vent doors not open on 2001 gmcsonoma
How to remove pentium cover on a 2000 gmc safari
Where do I fill the transmission fluid gmc Safari van?
Try using a higher size fuse you have a short in the wireing
Whrere is the spare tire located on a 1996 GMC Safari?
where is the fuel pressure regulator on a 1999 GMC SAFARI? thank you
The General Motors Company Safari Van was made from 1985 to 2005. The GMC Safari shared its platform with its sibling the GMC Astro van, which was very similar.
how u change spark plugs on 1998 gmc safari van