a good friend of mine gave me his 1994 Dodge Ram Van B250 5.2l with only 77k miles. i changed IC valve, MAP sensor, throttle positioning sensor, spark plugs, wires, distributor cap & anchor, but still have some issues with the AC turning off and defroster coming on. i read it's probably the check valve. i sure can't locate it. can anybody please hint me to it? also going to change EGR valve next week as idle is still not working properly. tried replacing fuel filter but the quick disconnect coming from tank is not opening so probably gotta saw it out with a hand saw. anybody has similar experience? any rec's on which service repair manual to get (online or original hardcopy as sold on ebay)? thank you.

 

You want a factory service manual. The digital versions are a LOT cheaper.....

 

If your 1994 5.2 is the same as my 1999 5.2 that check valve will be on the passenger side of the engine. You will have to remove the inside dog house cover and look close to where the intake manifold meets the block by the passengers foot if they were sitting in the van. You will see a rubber Z shaped hose fitting on the manifold with a larger rubber hose connected to it heading toward the front of the van across the top of the motor. That check valve is on the Z shaped rubber hose adapter. Pull it apart and suck and blow into the valve and see if its free in one direction and stops in the other.
By the way the vacuum damper control system for the AC and heat system will default to the defroster if you have a broken hose or vacuum leak in the vacuum control circuit.

 

thanks a lot Busted Nuckles. i should be able to find it. i did order the service repair manual just in case as well. also have to check the complete vacuum line with propane to see if there are any leaks (which there has to be). so far it has been a lot of fun, especially without having hardly information on the vehicle. but every day i manage to make it run better.

 

Mine had an actual break in one of the small vacuum lines leading from the switch. Exactly as Busted Nuckles noted. Handle with care. The lines want to turn to powder.
ETA: symptoms were the same... AC goes to defrost.

 

looks like this is the check valve, no? (white elbow valve)

check valve (white/dirty looking elbow)

check valve (white/dirty looking elbow)

 

Busted Nuckles, i see which one you meant (the black Z shaped one). isn't the white (grey) one also a check valve?

 

That white feller is the PCV valve. I am not seeing any check valves there, at least, not that I recognize.

 

 

In the middle of the Z fitting you can see the installed check valve. The other pic shows the check valve by itself. I dont see a check valve in your picture. I grabbed these parts at the junk yard but Im not sure what year van the were from. My 1999 has a check valve in this location. I think there is also another style that the check valve inserts into the end of the Z and the other side of the check valve connects to the hose. If your AC dampers are not shifting at all you have more leaks or broken lines like Block Head stated. Even if just the check valve is missing or bad sometimes at high vacuum your dampers should shift. Right where the vacuum lines go into the van in the firewall there is a rubber or plastic connector you can pull the old cracked and broken tubes off of under the hood and replace them 1 by 1 from that connector to each component under the hood. One runs behind the passenger headlight to a vacuum pod for fresh air inlet, one runs to the heater control valve and one is vacuum suction supply that feeds into the van to the controller. Thats out of memory on my 1999 5.2 liter 1500 van with AC. That should get you started anyway. Lol