Chevrolet Repair: Vacuum Leak diagnosis, chevy astro van, hvac control systems

Question
I have had continuing problems with air flow (both heater and A/C) thru my vents in our 1995 4.3 L TBI V6 Chevy Astro Van. I think its a vacuum related issue - because it will switch air flow from normal a/c vents to defrost under load conditions on highway (going uphill etc) and then correct itself when going downhill(air returns to front vents). I have had the heater/A/C temp control module replaced with no improvement.  My problem is trying to identify the vacuum line(s) attached to the intake manifold to look for a leak. My Haynes manual is worthless and I am not sure where to look and how to troubleshoot the problem.  Also, the heater is not working worth a darn - may be a vac activated switch issue also.  This is the second ASTRO van we have owned and I am not too impressed with the HVAC control systems on them. Can you help me with some tips? Thanks.

Answer
Hi Randy, I also had 2 Astro vans and had great luck with them. I sold them both with 160,000 miles and still going. Your problem is located where the rubber air inlet meets the engine throttle body. Look under this rubber inlet and you will find a black plastic vacuum line. It has a hole in it or is just falling apart. Replace this line from the intake manifold to the tee up by the A/C accumulator/dryer.


Have a Great Day    Mark