So, here's the skinny.... I have a 98 ram 1500 5.2l 2wd and When I'm running my AC after maybe 10mins the oil pressure gauge drops to 0 and the check Gases light pops on but goes back up to little under 40 when i get going again or turn off the AC. Even when I don't have the AC running and I just get off the highway or stop at a red light after driving a few miles the oil pressure drops and shots back up once I get going again. I've replaced the oil pump, rear main seal, and oil pan gasket and yet it's still doing this and oil is slowly leaking down into the transmission bell housing but there's no visible trail on the flex plate where the leak could be coming from, what else could be causing this?

Plus, now when I run the AC, all the air shots out of the defrost vents. I've gone through all lines to check for leak spots, nothing. Replaced the check valve, nothing. What could be the reason for this?

Is this all connected somehow?

 

Your oil pressure sensor is bad. Totally unrelated to the A/C problem. You have a broken vacuum line... Check the line by the upper a/c line where it goes into the cab, I bet that feller is broken.

 

Actually you have two, One right off the intake and the other by the ac lines(cowl). And you need to make sure they have flow towards the motor not away from it.

 

Replaced the oil pressure sensor, didn't fix the issue. And No broken or cracked vacuum lines anywhere because I replaced all this morning.

​​​​​​I do however hear the whistling noise coming from within the plenum but replaced the plenum and intake manifold gaskets last week because of this issue and it still didn't fix the problem. When I checked inside the plenum this morning there was no oil at all inside, bone dry inside the plenum.

Got any other suggestions?

 

Put both check valves on and still did solve the issue. Got any other suggestions?

 

Check the vac actuators to upper right of accelerator.

 

Did you put them in the correct way? Air flow or vac needs to flow towards the motor. If either one is reversed you will have no vacuum.

 

Yes they're on the right way and still nothing. There is a whistling noise coming from within the intake manifold but I've even replaced the intake manifold gaskets and plenum gaskets last week to correct this same issue but still no luck. I know for a fact that it's not the plenum gasket again either because its bone dry inside the manifold.
Any other suggestions?

 

Did you check the other vac lines? The one going to the cruse control actuator always cracks. Also check the line going to the reservoir under the cowl. Check vac at the second check valve where it goes into the cab, If you have good vac there(engine running) the problem is in the cab/hvac box.