I need some help guy's, I have a 1997 Dodge Ram 1500 4X4. The problem is that when I turn my air conditioning on it wants to blow out the defroster vents untill enough pressure is built back up and when I go up a small hill the same thing but the it cuts off completly and goes out the defroster vents again until enough pressure builds back up. I've relpaced the check valve.

 

we just discussed this topic. look for the topic uphill, no ac downhill, ac. its probably the same issue. a vaccum leak is most likly the problem. the defroster thing is a safty issue. if you develope a vaccum leak, instead of no ac, it allows the defroster so the windows dont fog up. look under the battery tray, bet its that one.