ADD confusion...no 4wd

[Whitey0817]

'95 3.0 auto/add' - So my 4wd quit working, was fine until it snowed the other day, go figure. T case lever functions fine and will engage low range, just no front axle spin. The ADD relay does click under the dash, just nothing after that. Am I reading correctly when it says both the t case position and pressure switches are both needed to activate the ADD relay? Meaning those 3 components are working? I've been reading too much and I think I need a fresh brain...I also thought I read the ADD switch on the front axle must complete the circuit before the actuator will engage? Any help on where to go would be appreciated, and like I said everything worked normal just a few weeks ago

 

[KidVermicious]

Check for vacuum at the front axle. Should be on one side in 2wd and the other side in 4w, but I bet you've got weak or no vacuum on the 4wd side.

 

[mikebontoft]

I agree with kid, as I was about to suggest the same.

 

[fourwd1]

The switch on the actuator signals that the actuator is in the locked position and completes the circuit to light the 4WD light on the dash.
Chances are there is a problem with the "lock" Vacuum Switching Valve or the vacuum lines themselves. The rubber lines get hard with age and crack, or could just have come loose.
Or the rubber diaphragm in the VSV could have gone bad.