Astro air vents fail when accelerating uphill

rpoling

I have a '97 Chevy Astro van, AWD, 80k miles. Recently, while accelerating uphill, the airflow stops coming out of the 4 upper air vents on the dash. This includes Vent and A/C. Air continues to flow from the lower vents as well as the defroster. The airflow returns to normal when I stop accelerating, or go downhill.

A friend told me that it is probably a vacuum leak. My question is.... how do I find and repair this leak?
Any ideas? Thanks!! Rick

dpwestlake

Volvo's do the same thing. they have a cut off on the AC. The same will happen if you accelerate hard on a level road. Check your manual.

0patience

Whether the check valve at the brake booster is not working properly or you have a crack in one of the vacuum hoses is the question.
One check, start the vehicle, let it run for a bit, then shut it down, wait a couple minutes, and pull the valve at the brake booster. You should hear a decent hiss from it. If you don't. the check valve is bad.

How does it idle?
How are the brakes?

Mr_Shiftright

Yep, I'm with Opatience on this one...vacuum leak is closing the upper vents as vacuum drops (under engine load).

poisondartfrog

Same problem happened recently on my '93 Pontiac Grand Prix. The hard plastic line to the vacuum (reserve) bottle broke. The a/c would switch to the floor during acceleration. It also prevented the fuel purge solenoid from working properly, too. My gas cap would hiss after shutting off the car... unnerving!