Howdy ladies and gentlemen. I recently installed a Flowmaster American Thunder cat-back exhaust system on my 97 Ram 1500 4x2 ext. cab with a little over 53,000 miles on it, and I've noticed that sometimes at highway speed (70-80) my air conditioner stops blowing any air at all. Whenever I lay back off the accelerator, the AC kicks back on. Anybody have any suggestions on what the problem might be?

 

Next time it happens, reach up and see if the air is coming out of the defrost ducts.

Vacuum-controlled HVAC units revert to defrost (as a safety system) if there is insufficient vacuum to the actuators. If that is the case with yours, you may have a vacuum leak somewhere.

Could be as simple as a cracked hose, or up to a leaking intake plenum pan gasket.