I have a 98 1500. I was having an issue with my A/C, every time I tend to apply pressure on the gas pedal it will cut the flow from the "head" vents and switch it over to the defrost vents. Then as I release the gas it'll switch back. It used to do it every once in a blue moon but as of lately is been everyday. It seems like it could be pulling a vacuum from somewhere but I'm not positive so that's why I'm coming here to see if ya'll might have a better idea.