I have a 1997 Dodge Ram 1500 5.2l 4x4 with cruise control. I have recently just done the intake plenum fix. I rehooked all the lines correctly. I have all the lines hooked up like they should. I checked all the lines for leaks, no leaks at cruise control line or thing under battery. checked other lines to transfer case, to the firewall and vacuum reservoir. No leaks. The line that goes into the firewall and into the cab doesnt sound like it has a leak. I pulled both check valves off and I can blow one way through them and the other way you cant so they are good. I cant get the vents to switch at all. My 4x4 works and will engage and my cruise works. I do notice sometimes when i switch it to face vents that i can hear a hissing noise right at the middle of the dash behind the switch but not from the switch. This weekend i did remove both check valves and checked the switching and it switched but when i drove to school the next day it would not come out of the face vents. Any input would be much appreciated and I have read quite a few threads on the internet but just cant figure it all out.

 

Check valves installed backwards? They need to flow TOWARD the intake.

Welcome to DF!

 

Yes I did that at first because I disconnected the line after the second check valve and was getting no vacuum them switched them around and now have vacuum there. Then reconnect it and still vents don't switch.

 

Wonder if the line broke in the cab somewhere.... the plastic lines were an interesting idea, but, as they age, they get really brittle, and break incredibly easily. Could pull the control head out of the dash, and see if you are getting vacuum there. (my guess would be "no".....)

 

hey big blue,
try checking the control switch in the dash, CAREFULLY remove it , top is control **** for floor, dash, defrost has all the vac lines running to it...inside the rectangular box is a series of tiny tiny holes be REALLY CAREFUL taking apart... mine were clogged with the grease thats in there from factory 20 years ago along with dust, degrease the housing keeping a touch of grease to re grease the slide , check the vac lines and reinstall keeping the **** and the little slide part in defrost [to the right ] if you follow that back towards engine you`ll see a clear plastic connection with all the vac lines running into and out of check these, from there the yellow line runs to the actuator that controls the door for the floor,dash, defrost has a metal arm running up to it CAREFULLY remove the arm unscrew and remove actuator check it, and the little plastic clip that moves the door see if door will move/ be careful dealing with these plastic parts could be a real pain if they break ...good luck let me know if it works ps also have a few more ideas....