I took apart one of my HVAC Actuators because I can't leave well enough alone. Also thought this would be good for the archive.
I have loaded two pictures. In them, you can see I am checking the feedback potentiometer. I am using pin 9 for the positive lead of the meter and pin 6 for the negative lead of the meter. If you take the gear out that drives the control door you can turn the potentiometer and find the over load spot. When I say over load (OL) on many meters, I mean infinite resistance. Just like having your meter leads unplugged. You don't want to start there. It will mess up the calibration of the HVAC computer and shut down your actuator. You want to be just off the OL and the meter should read around 504 K Ohms (504,000 ohms) on one side and when you rotate the potentiometer in the other direction you should get 497 K Ohms (497,00 ohms). Now, the tricky part is getting the door drive gear back in and getting the calibration right. Just remember, you want to START at one extreme, meaning the door drive gear against one stop with about 497 K Ohms or 504 K Ohms. Then insert the door drive gear, once meshed, rotate the gears and make sure the meter stays is a nice uniform curve (rise or fall) of resistance with no over load (OL) or infinite resistance noted. Once you have established this relationship the feedback circuit is golden. Reinstall remaining gear/s and reinstall the actuator, then recalibrate the system. I would like to note, this actuator was the Mode Control Actuator, but I also compared my Defrost Door Actuator and the values were the same.
Keith
I have loaded two pictures. In them, you can see I am checking the feedback potentiometer. I am using pin 9 for the positive lead of the meter and pin 6 for the negative lead of the meter. If you take the gear out that drives the control door you can turn the potentiometer and find the over load spot. When I say over load (OL) on many meters, I mean infinite resistance. Just like having your meter leads unplugged. You don't want to start there. It will mess up the calibration of the HVAC computer and shut down your actuator. You want to be just off the OL and the meter should read around 504 K Ohms (504,000 ohms) on one side and when you rotate the potentiometer in the other direction you should get 497 K Ohms (497,00 ohms). Now, the tricky part is getting the door drive gear back in and getting the calibration right. Just remember, you want to START at one extreme, meaning the door drive gear against one stop with about 497 K Ohms or 504 K Ohms. Then insert the door drive gear, once meshed, rotate the gears and make sure the meter stays is a nice uniform curve (rise or fall) of resistance with no over load (OL) or infinite resistance noted. Once you have established this relationship the feedback circuit is golden. Reinstall remaining gear/s and reinstall the actuator, then recalibrate the system. I would like to note, this actuator was the Mode Control Actuator, but I also compared my Defrost Door Actuator and the values were the same.
Keith