Vent actuator intermittent

[Shdwdrgn]

I've noticed a couple times recently that the AC won't blow from the front dash vents, it only comes out from the floor. Changing the modes, I can get a bit of air to come out the top of the dash, but other switching between modes has no effect. And yet if I stop the truck, then start it again, everything works just fine. Since it typically changes between modes without hesitation and the restart fixes the problem, I'm thinking this may be more of a sensor issue rather than a mechanical failure of the actuator? Anyone have thoughts on what I might check?

 

[linneje]

The actuator controls a blend door that diverts the air according to the choice you make. In working with my rear blend door actuator I noticed a couple of things:

1) It takes a lot of force to move the blend door when the fan is on high. I tried moving it by hand with the fan on high and I could not, I felt like I would break the pin attached to the door (the pin slides into the actuator so that the actuator can turn the door).

2) When I put in my new actuator I thought that I had the actuator installed correctly because I tested it. However, when I drove with my family, it worked for a bit (air on the faces in the rear), but then it suddenly reverted back to floor air without touching the controls. My guess is that when it turns the door, even if successful if it encouters too much resistance (it is still trying to turn the door even when reaching the limit) it will revert back to some default position. This all occurred because I had broken off part of the pin so I had trouble getting it installed correctly.

The simplest thing would be to get it to recalibrate, and see if that fixes the problem. Another would be to turn the fan down low before changing the mode, and see if that works. You could have a problem with the blend door (like debris in there or some part broke off) that is causing increased resistance.

 

[Shdwdrgn]

Actually the fan was not on high when this happened, although I did try manually running the fan speed up and down through the range. I also tried the recirculate mode and the defrost mode. Nothing seemed to make any difference, except simply turning the vehicle off and starting it back up again. Debris in the system is certainly a possibility, given the age. If it keeps happening, I may have to resort to opening it up one of these days to see.

 

[Mooseman]

Try resetting the system by pulling the HVAC-B fuse for a bit, putting it back in and turning the key to RUN but don't start the engine. Leave it alone for a couple of minutes while it recalibrates. If still no luck, then it's probably a dead or dying actuator.

 

[LA4x4TB]

The same thing happened in my Sierra. The actuator was easy to reach, so I tapped it with a screwdriver handle. The gear started up and the blend door opened. It's random but frequent enough that I'm going to replace the actuator soon.

I don't know if the actuator is easily accessible on the TrailBlazer, but if recalibrating doesn't work, you could give it a try.

 

[MDBT]

Try resetting the system by pulling the HVAC-B fuse for a bit, putting it back in and turning the key to RUN but don't start the engine. Leave it alone for a couple of minutes while it recalibrates. If still no luck, then it's probably a dead or dying actuator.

This appears to have fixed my intermittent issue with the passenger actuator where I would get hot air during A/C that would sometimes go away after shutting the vehicle off and back on. Definitely worth a try before picking up parts.