Hi, so I have a 1998 ram 2500 v8 (gas) and air only comes through the defrost vents. I know this is a common issue and i have extensively researched it. I replaced both check valves, replaced half of the vacuum lines, and checked every inch of them for cracks/breaks (except for under the dash). But still, air only comes through defrost. I even ran a vacuum hose from the 2nd check valve directly to the switch inside the cab. I've made absolutely no progress. The cruise control doesnt work and the light doesnt even come on either. 4x4 works just fine, so I at least know I have vacuum somewhere. Any help from someone with more experience than myself would be much appreciated, thanks!

 

Cruise control could be electronic or the servo. The vents could be bad control unit or a bad actuator on the box

 

Well, the control unit will turn the vents on and off as well as control the fan speed and heat vs ac pretty well. So I think it is working ok. Do you mean the blend door actuator when you refer to the actuator box?

 

Still check the switch vacuum can leak from the switch. No not the blend door ,(that controls temp) I mean the mode selection door on the HVAC box

 

Might want to make sure you have the check valves in right. If they are in the wrong direction you will have no vac. If you have a vac gauge put it on where the reservoir is and see what you have.

 

This is what I was thinking as well. I believe the arrow on the valve points back toward the intake manifold. (vacuum source.)

 

Is the actuator you were talking about the same thing as the control unit? And I know i have the check valves in correctly.

 

Are they new or the ones that where in the truck? If they are original they may be bad. The replacements from napa have nothing on them. You have to figure out witch direction it will allow flow(vac) and go from there. There are more than one "actuator/s"(things that move the air flow doors) Some are spring loaded and will not move unless there is enough vac to compensate for the spring pressure. The control unit only switches the vac to the actuator/s needed for what position you want (floor vent defrost etc...)

 

I bought some new ones from orielly and put them in the same direction the old ones were in. I just blew on the ends and whichever end would flow freely vs resistance to blowing i put in the direction accordingly.

 

Start the truck and pull the vac line off of the one up by the reservoir. The line going threw the firewall and see if you have vac there.