Hey Sparky, just need some help with 2002 Suburban a/c blowing to defrost only.

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#15655 In Progress 2002 Chevrolet Suburban 1500 public

I know you addressed this before and I tried to follow your previous tips but the door mode actuator would not move.
Took it out and found a broken gear/cog inside.
I replaced with new actuator but same problem.
It does not move from defrost position.
It was in front vent position out-of-the-box but immediately moved/defaulted to defrost when powered on.
Jumping the gun, I also replaced the in-dash control module head unit thinking it was a bad pot.
Same problem, so I tried to troubleshoot as I should have done before.
I checked the voltage on each wire with the new parts:
Brown – 12V
Black – ground
Gray – 5V
Red – 5V constant (but actuator doesn’t move.)
White – 2.5V constant regardless of dial position.
I reset by removing the negative battery cable and following the instructions.
Tried several times but not successful.
Went back to the old actuator and repositioned the internal gear cogs to somewhere near the front vent position and reinstalled.
It now cycles every 7/8 seconds back and forth.
Again tried to reset per your instructions but no change.
Doesn’t seem to find home successfully, maybe because of the broken gear and misaligned internal timing.
Although as I monitored the voltage readings during the cycling, this time the Red and White wires alternate normally in the variance you specified without touching the dials.
Just never stops cycling.
I have two DTC faults that will not clear:
B1020 – Auxiliary ECU Malfunction
B3761 – Air Flow Control 3 Feedback Circuit
Not sure why I get different red/white wire readings with the two actuators unless both are bad.
Any ideas?
Is testing with actuator plugged-in hanging down acceptable? Watching he movement.
Or does it have to be completely installed for a legitimate test?
Thanks for your help.


I have been mulling over your data and my initial conclusion is that the replacement actuator is either the wrong part number or the part is faulty.  However, I need to point out that allowing the actuator to just hang down while testing is not a valid method and could be part of your problem. You see the control system during recalibration and during regular use has a preset range of travel. If the actuator travels beyond that limit it will automatically default to the defrost position. During normal operation the slot in the actuator shaft stays within the two hash marks that are cast into the actuator housing. That range of travel is approximately 90 degrees.  Along this line of thought some vehicles had to have new programming installed in the control panel to adjust  the travel range. This was updated by GM to account for compression/wear on the foam door surfaces that would allow an over travel condition as well.

So my plan would be to double check to make sure you have the correct part. If confirmed to be correct I would make sure the new actuator is adjusted so the the notch in the actuator shaft is centered between the two hash marks and then re install, it and perform the recalibration procedure. On your vehicle the radio fuse has to be removed and reinstalled to start the procedure.


Thank you.
Attached are pictures of my actuator.
Are you saying the slots in the metal sleeve need to align with the white dots?
The only way I see to move it without breaking is to open the cover, remove the transfer gear, rotate the actuator shaft and reinstall the gear.
Is that the correct procedure?


Since you already have the actuator off, disassembly and repair is the best choice.  I have included an image of a new actuator as a reference for where the gear cog should be positioned in relation to the actuator body.

There are two different internal designs to be aware of. One has a metal contact with multiple fingers attached to the bottom of a gear. Those contact fingers correlate with carbon traces on the circuit board. The other design uses a small gear driven potentiometer.

The first design is easy enough to properly orient since you can see where the  contact fingers need to be positioned. The second is a little bit trickier because you need to make sure the potentiometer is electrically centered. It has been a long time since I have dealt with centering on the potentiometer style so I would recommend taking your time during disassembly. Take pictures of the internals and upload them here so I can see what you have.

Thank you.
It looks like the potentiometer style to me. I could not turn back the actuator arm without fear of breaking something. The only way I saw to correct the overdriven arm is to remove the white transfer gear and turn back the arm while still keeping the mesh with the pot. So at least I think it is back to the factory setting now. The attached picture is after I had done this. How can I make sure the pot is electrically centered? Is there a marking or will that require taking readings from the contacts of the pot?
Thanks again.


It should be good there. So now you just need to mount it before connecting the harness to it.

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