I am stumped. Apologize this is long. I have read and re-read posts and nothing seems to help me figure out my issue. I have two issues 4x4 does not work and the hvac blows out the vents only. Not really after how to fix the 4x4 right now, but more concern on the hvac system.
*It blows hot and cold out of vents only. The fan control works. The temp control works. The mode control does not. I can not get it to switch to defrost or floor, it stays vent all the time.
*I then searched for the vacuum hoses under the hood and this is where it all begins :-(
*I found the vacuum hose to the vacuum storage tank (in the fender) was rotten. I traced the vacuum line to the manifold. It was rotten and it was not connected to the pcv valve cover and it was broken too! It look liked it was not even the right hose and connection.
*I replaced the pcv valve cover and ran a new hose to the check valve.
Ran a new hose to the vacuum tank in the fender. Re hooked everything up and !!!!! Still no go. I noticed the hose to the fender came off easy. So I just plugged it for now. Still does not work properly.
*I put my mighty vac onto all the colored vacuum lines I could find and tested them. they all held vacuum. I tested the actuators too, they hold vacuum.. They all appear to be good and hold vacuum.
*SO how do I test the actual control panel. I think it is electrical and in the control panel since I can apply vacuum to the "mode" actuator (drivers side top actuator with yellow and brown tubes) and I can get it to switch to defrost and floor.

So any words of wisdom?

 

Sounds to me definitely like a vacuum issue. Need to check vacuum line for 4X4. If three button check the line down to vacuum switch on top of transfer case and back to actuator under battery. If 4 button the vacuum switch is located on firewall, then line runs down to vacuum actuator under the battery. If any of these are rotten you would be losing your vacuum and HVAC would only blow through vent.

 

I have that line plugged off. I can pull a vacuum to all the lines to the HVAC system. When in Defrost it holds a vacuum. When changing to floor or vent I lose vacuum and can not pump it up.
I did grab a another controller out of the salvage yard cheap. It did not help, except now I have lights that work :-)
What runs the vacuum manifold? That seems to be what is not switching?

 

More than likely a vacuum routing problem. What year, make, model, is the vehicle? Manual HVAC or automatic climate control? 3 or 4 button 4WD switch on the dash? Always helps if we know what you're working on

 

sorry.
1998, Blazer, Auto Air, 3 button.
I think I have narrowed it down to the Mode Door Actuator. If I manually move that door, everything works. All the actuators move or at least try to move. I took the mode actuator off and it is not smooth at all. It does hold vacuum but it jerks on the way in and out.

 

There's a flexible rubber gasket attached to the edge of the door. It can dry rot and start to crumble which makes the door bind up. Unfortunately, the heater case has to come out, and apart, to fix it. That requires removing the entire dash, which is about an 8 hour job, (if you're familiar with it).

 

If that is it, I guess my daughter will live with it. LOL I can move the door myself pretty easy.