this has to be a common problem! My a/c blows out the defrost when i push on the gas pedal then goes back to the vents when i let off. Any ideals out there.

 

what truck do you have? I had that problem in my 98 and it was a bad check valve in the vacuum line. look under the hood on the passg side of the truck on the firewall, a hard tube will run out and down, find the check valve and see if its bad (blow in it from both sides, only one way should let air through) if it is bad, then just replace it. if that doesnt work, then there is a leak somewhere.

 

Until recently automotive vent controls were powered by intake vacuum. WTO throttle causes the intake vacuum to drop low enough that the actuators relax or drift. Closing the throttle restores vacuum. Don't know if that is the case with your truck but it is common with older models.

 

thanks for the info. my truck is a 98 ram with a v6 and my friend has a 99 with a v8 and they both do the samething. what your telling me sounds like my problem. when i ride down the road and give too much gas pedal the a/c blows out the defrost. some one told me it could be a check valve on the passanger side of the truck. what do you think would be the fix for this problem
thanks

 

The check valve should be a small plastic geegaw with tubes sticking out either end.
Changing it shouldn't be difficult.