I have a 1992 S-10 Blazer, A/C works good except when I accelerate the air stops coming out of the dash vents, instead it comes out the defrost, now if I take my foot off the gas it comes back to the dash vents it even comes out of the floor vents when I accelerate. Any ideas what it could be?
Thanks
Joe

There is a vacuum leak in the HVAC system, or the vacuum check valve is faulty. The check valve is inline, under the hood. Follow the vacuum lines to and from the vacuum reservoir and you'll find it. It should pass vacuum in one direction only. Most auto parts stores have them in the Dorman "HELP" line and cost is under $5.