I have here the blend door step motor that controls airflow into the heater core compartment. I want to test it to make sure it still has 100% of it's range. I suspect the door might not be all the way closed and some heat is mixing with the vent.
I thought maybe I could take a 9v battery to it, but I'm not sure which pins do what and I don't want to trial and error this because I may short something. Either that or the 9v batter just won't power anything if it's a 12v requirement.
I've got a bit of reading to do on this. I just wanted to poke someone's brain about this if they already know something.
I might actually take this question over to Stack Exchange since this isn't Blazer specific.

 

Easiest method to check travel is to re-connect to the Blazer, then with key ON or engine running...does not matter. Turn the temp control from full cool to full hot and watch to see if the slot moves between the two lines on the case.
Another method is to take the case off, apply 12V directly to the small motor terminals. Problem with this method is that you have to be careful or you will get the slot out of synch with the two lines on the case. This is just a small 12Vdc motor, so you can always reverse the power to run the motor in the opposite direction. This is useful when there is broken teeth on the gear...this way you can rotate the gear to use the teeth on the other half of the gear and not have to replace the actuator.

 

Powering te vehicle might not be a practical option right now. I still have the dashboard pulled out, so I'd have to remove the wire harness and fuse box from the dash to hook all of that back up to run the AC control panel and operate the blend door motor.
I'll look into applying a 12v power supply to it instead. But I too have concern with breaking teh calibration of the gear set.

I opened the motor assembly and found that the main gear does appear the be split on one side. Turning the gears deteched from the motor, I do feel resistance when the connecting gear runs over the split. I pulled the gear and rotated it 180 degrees so the split doesn't doesn't come in contact with the other gear. I'm not too worried about runing the calibration because I found a stopper that prevents the main gear from rotating out of bounds. Though my other concern is the blue gear. The blue gear is connected to an chip on the PCB. I'm guessing this is a position sensor that tell the motor when to stop. I hope I didn't ruin the calibration by allowing the blue gear to turn. Though I guess that depends if this position sensor measures absolute position or realative position. Without knowing how the body controll module is programed, I can't say what the expected behavior is.

Though then I guess I'd have to ask: how would you install a new actuator without calibration? I guess the system sorts itself out?
Dang, now I am attempt to pull the dash wire harness just to hook everything up and test.


Motor and gear assembly



Split main gear



Pulled the gear from the center piece and rotated the split



Connector with 3 wires for the 4 pins

 

there is a calibration procedure..I think it involved pulling out the radio fuse for 30-60 seconds or something along those lines..I am sure someone will chime in with a better memory than I or it may be already (betcha it is) be somewheres on this site...It is in the GM manual as well..If you need me to (if nobody else chimes in) I can look it up.....Jerry

 

From what I remember, the position is relative, not absolute. But those slots in the main gear have to align with the tabs on the actuator arm.
However with the main gear split like that, I think you are looking at replacing the actuator unit as the main gear may just slide on the center shaft instead of moving the actuator arm.

I know new actuators come aligned at either full warm or full cool, just have to match the temp setting to the actuator position.

And yes....three terminals in the connector...going to four pins in the actuator.....???

 

So as it turns out the actuator is self calibrating. At least this OEM one is. I did what LannyL81 suggested and tested the actuator and blend door in the truck with the power on. I wanted to rewrap the wireharness for the dashboard anyway, so I pulled that out of the dashboard so I cna hook everything up and test it.

I was curious to see how far left or right the door would swing
I had the switch set at 50% to start, the door's position when I reinstalled the actuator was about 95% cold and 5% hot. When I had power turned on, the actuator moved to door to about 30% hot and 70% cold with the switch at 50%. The calibration is obviously off. I turned the temperature switch towards the cold side more until I saw the blend door at 100% cold. The door at 100% and the switch at 70% cold and 30%. I then turned the switch to 100% hot and watched the actuator move the door to about 90% hot and 10% cold, and then back to cold until the door was 100% cold. In doing this and observing the behavior, I noticed that whenever the motor met resistance, it would back off and not over torque the gears. So I took a leap of faith, set the switch the 100% cold, and watched what the actuator would do. Nothing broke and both the switch and door were at 100% cold. So I went back to 100% hot on the switch, watched the door move to close off the cold side and it met resistance adn backed off the same. After doing this a few times, the actuator calibrated itself and learned where the range is for 100% cold and 100% hot.