I have a 98 Ram 5.9 ext cab 4x4 1500. When i have the a/c or even the vent blower on, under the slightest accleration all cool air stops. When i let off the gas, i can hear the blend door slam shut. Even does it without the a/c being on just vent blowing.
Any ideas what i can do to fix this?
Thanks

 

Vacuum leak.

 

A leak, as the venerable mister jkeaton has said, or a blown vacuum check valve. Try searching the forum for "wild vents" to get a good starting point figuring out which.

 

For me, it was the vacuum line chaffed through there it goes through the firewall with the A/C lines.

 

That will give me a place to start lookingg. Thanks