My father in law has a 97 ram 5.2 L and when he steps on the gas the AC switches from vents to defrost. I have read in this forum that it is due to a vacuum leak. Any idea which hose or at least where we could start to look for the bad line?

there are vacuum lines on the back of the defrost/vent switch, start there

I have a 95 Ram 5.9L with the same problem and just completed the Climate Control assembly vacuum check. All 5 vac lines (black, red, green, yellow and brown) are holding 8 inches (wg) and the check valve, located under the hood pass. side of intake manifold, tested OK. At this point it is an intermediate problem and I'm convinced its the Climate Control Assembly in the dash, will replace tomorrow.

what did you use to check that?

what did you use to check that?


I used an automotive hand operated vacuum pump (Mityvac p/n 04000) which I picked up at the local Auto Zone (tool rental program).

Your problem is the one-way vacuum valve on the side of the throttle body. It should only let vacuum pass in one direction but yours it worn out so when you press on the throttle its forcing the air to go the other way. its like $8 at dodge. dont waste your time looking for one at autozone(atleast they didnt have one near me) a ford style one should also work fine. The valve it located on the passenger side of the engine. you will see a vacuum line coming off of the throttle body(or intake manifold I cant remember) . this line runs to the egr solonoid and a few other things. (I cant actually remember what else) the valve is about 2" long it looks like a vacuum conector with a round flat spot in the middle. if you cant find it email me at whitekknight@hotmail.com and I will look at a truck tommorow and possibly take some pics or give you a more accurate location

GL

i had that problem,vac was my cause. hose was cracked located drv. s. under battery area. bend the thin hard hose it will prob snap easyly, change it to rubber, , let me know if i help you