Climate control vent settings not changing
 

My air vent controls have not been working. It seems to be stuck on vents and will not change to defrost and foot. No matter what it is set to it will blow from main vents and a little from defrost. It also does this with the climate off, it will blow air out of main vents.

I had read on another thread that the vacuum line that goes into the nipple between ABS module and Cruise could be not connected. Low and behold mine was dangling with a screw in the other end. So I connected it onto the nipple and my issue still persisted.

I then saw that the small hose in the middle of it is a usual suspect of being worn out. After messing with the hose it left my fingers black, I can also feel multiple cracks in it. I will be replacing this soon however I just want to get a few opinions.

I have read that the vent controls are controlled by a vacuum actuator behind the dashboard and on one thread it was said that if you change the knob and hear it hissing then the actuator is working. If I change my knob to foot or regular vents I can hear it hissing, I cannot distinctly hear it when I change it from either of those to defrost.

Either way I just wanted a few opinions on wether you think this vacuum line alone could be the culprit or if the actuator is bad aswell.
https://cimg2.ibsrv.net/gimg/blazerf...bef430c82.jpeg

What year, what sort of climate control (Computer or manual), and what type of transfer case do you have (3-button or 4-button with Auto 4wd)?

But to your question, almost always HVAC problems are due to leaks in the vacuum lines in the engine compartment. The ones under the instrument panel are pretty durable. The climate controls fail rarely. The lack of vacuum will also disable the front axke engagement for 4wd.

2000. The climate controls are manual and I have the 3 button transfercase. Just had a snowstorm and my 4wd has been working just fine.

If your front axle is engaging, then perhaps you do have a problem with your HVAC control box in the instrument panel. These are not very hard to replace. I have to replace mine due to the lights being out in it.

Should I also replace the mode actuator just incase that is broken aswell?

With the instrument panel off, you can test the vacuum actuators with a hand vacuum pump like a Mityvac. This could help you find the origin of your issues.

These links has some discussion of the vacuum hose routing, but it is for 96 and 98. https://www.john-stichnoth.com/AirOutTheVents.html http://www.john-stichnoth.com/SonomaT-caseSwitch2.html

I've attached a diagram I found or a 2000 that might also help.

Good Luck and be sure to ask questions and report back on what you find.

Thanks, Christine

Also, after messing around with my climate controls here is how the switch is working.

The AC foot and dash vents work fine and blow out air to whichever is selected.

When I switch to any of the heater vent options they all make a slight hiss from behind the switch however the AC options do not. The foot vents only work on AC.

With this considered I am leaning towards a vacuum line on the switch has been disconnected? Might I aswell just replace the whole switch?

Some good pics here https://blazerforum.com/forum/2nd-ge...30/#post733994

I changed both the control box itself from the dash, the vacuum lines under hood, and the valve for the vacuum line. Nothing has changed and the problem continues. Going to look at actuator this week.

Took the actuator for the mode door out and it is junk. Autozone has part Dorman 604-923 but it looks like it doesn’t have the second clip like the factory one does. I’ve looked at some old threads and the links are dead and the only one I found (acdelco #15-72684) isn’t for sale anymore.