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O/T GMC van air cond.

A

Anonymous-0

Well-known Member
My 99 gmc van air cond. cuts off going up a hill, and comes back on on level road. The controls are operated by vacuum, which goes down going up a hill. I can't locate the vacuum leak. My wife is driving me nuts over this problem. Any suggestions. Stan
 
Stan,

Unless the "problem" is very, very, VERY noticeable, that is a normal occurrence.

'Tis the way that they are built. The compressor shuts off and at times the vacuum reservoir will run out of capacity under extreme, heavy demand.

If you can feel the mode doors changing where the cold air actually changes to heat, there "could be" a drivability/engine tuning/plugged exhaust problem, but it is doubtful.

Been thru this argument many times with many customers on lots of different makes of vehicles; many, many of them less than a month old.

Allan
 
Are you saying the air turns warm or the system is changing modes ie switching from the dash vents to floor and or defrost? If you're having mode changes, the vacuum check valve is likely failed. Its normally located in the vacuum line that goes through the firewall near the evaporator case. Make sure there are no cracks or breaks in the vacuum supply line. If it's turning warm going up hill, you may have an engine performance problem. Check the simple stuff like dirty air filter, worn spark plugs, under inflated tires, unload the extra weight, etc.
 
I know exactly what you are talking about although I can't help you. I had a ford van of the same vintage that did the same thing. it was apparent that it was vacuum related because of the way it went on so soon after cresting the hill. Mine had been wrecked before I bought it so it was probably tubing damage related to the collision.
 


I had the same problem with a Jeep Cherokee. Mine had a check valve in the vacuum line to the storage can that went bad, so on a high load situation the A/C system would lose vacuum.
 
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