HVAC Actuator Pics

blwn31

Original poster
Member
Jan 26, 2012
12
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
 

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blwn31

Original poster
Member
Jan 26, 2012
12
Please disregard my previous post.

I have edited my previous post and attached it here with new pictures, sorry for any inconvenience I may have caused.
After much fiddling and reading of my wiring diagrams I discovered I was on one of the wrong pins. The correct pin out should of been pins 7 and 9. This gives a much broader resistance reading through the potentiometer.
If you take the gear out that drives the door drive gear, you can then take out the door drive gear and turn potentiometer gear 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 .470K Ohms (470 ohms). Now install the door drive gear, at full CCW rotation you should be reading 470 ohms , and when you rotate the door drive gear CW, you should get 8.20K Ohms (8,200 ohms). Now, the tricky part is adjusting the door drive gear to the potentiometer gear and getting the relationship correct. Lightly pull up on the door drive gear and rotate the potentiometer gear a tooth of so and re-mesh the two gears. Just remember, you want to START at one extreme, meaning the door drive gear against one stop with about .470K Ohms or 8.2K Ohms. Now 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 should be close to golden. Reinstall remaining gear/s and reinstall the actuator, then recalibrate the system. You may have to adjust it a tooth in either direction to get the value the HVAC Module is looking for. Remember, always recalibrate after every adjustment, since the module remembers the actuators settings from the previous calibration.This particular actuator was off by one tooth and that was enough to shut down the actuator.
I must also note, not all actuators have the same resistance but, the same principles apply.

Keith
 

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