I don't think anyone cares anymore where stuffis posted anyway and this is old bodystyle(96+). My truck won't switch to the a/c vents. Got the heater out the bottom no prob and the defrost but when i put the A/C it won't switch to the dash vents. The town truck I drive does the same thing so I'd be fixin two. Anyone else have this problem ?

If you look under the dash(middle of the dash upper)on the drivers side there is an actuator(motorized) that diverts the air to the desired vent.More than likely the shaft has fallen out of the locating slot or the link has fallen off.

Yeah, I have the same problem Mode vent selection doesn't work. Been slow and erratic for a while. I also have problem with compressor engaging.

Per my helm manual....

To diagnose the mode actuation motor pull the plug at the motor. Key on run blower on Lo. Probe the number 8 socket. Looking at connector face with clip up its the top row third from left.

Measure voltage to ground while switching the vent selector. It should be smooth variable voltage. I don't know but assume 0 or 5 to 12 ish volts somewhat linear??? If constant, no or erratic voltage it goes on to check grounds and wiring and if connections are good it says to replace the main control board.

I measured erratic voltage approx 6.52 to 7.19 volts +/- a bit and it wasn't linear did not seem correct.

If smooth voltage then it diagnoses wires and connections and if all ok replace mode actuation motor.

I have never been inside duct work to know what actuator rods look like or how they work.

I am currently going to do mine approx $140 at dealer waiting on part.

My thread
http://www.dieselplace.com/forum/showthread.php?t=241890

You said that the "town truck" is doing the same thing. If the "town truck" is a gasser, then the problem is with a vacuum line most likely. Our diesels don't use vacuum for this function.

You said that the "town truck" is doing the same thing. If the "town truck" is a gasser, then the problem is with a vacuum line most likely. Our diesels don't use vacuum for this function.
I think the gassers are the same. Looks the same with wires and acutuator motors.

as far as i know , all this body style used electric motors for this job

I updated my thread but if it you missed it the control board cured my mode selection issues. My fan seems stronger too. Check my thread for part numbers.

Had the town truck fixed by Fleet Main. They said the door in the airbox was badly corrodeded and hanging up. I can see that because the truck sat for 6 months while they hired me but doesn't help me on mine but maybe same problem. Mine sits alot. I only use it for firewood and plowing the driveway.