2002 Chevrolet Suburban-Mode Actuator Cycles Between Vent & Defrost

SDixon: I had an issue with my vehicle back in August. I replaced the battery, upon new battery being installed the delivery mode actuator would cycle between defrost and vent every few seconds. I was going on vacation so had a local mechanic look at it. He informed me that the actuator was bad. I had him replace it. Once I got it back it did not fully actuate to floor or defrost, no matter what setting it was on it was blowing more out the vents than it was on the setting it was supposed to blow out of. I took the actuator out and lined everything back up and tried to calibrate but now it is cycling between defrost and vent again.

Sparky: At this point my suspicion would be that the actuator may not have been changed for whatever reason and you merely realigned the original faulty actuator. Can you get a clear picture of the actuator and upload it here?

Going past that do you have a voltmeter and the ability to use it for further testing?

SDixon: Not sure how much of the actuator you want to see. Here is one picture please let me know if you need something else or a different view. I do have a voltmeter and have a little ability with it. I unplugged the actuator last night when it cycled to defrost as we had frost overnight and I was needing the defroster.

 

Sparky: That actuator has been replaced and looks like it is what currently comes in an ACDelco box, part number 15-73952.

1. Testing at the mode actuator, key on, back probing with a Digital Volt Ohm Meter (DVOM).
2. There should 12 volts on the Brown wire.
3. There should  be a good ground on the Black wire.
4. There should be 5 volts on the Gray wire.
5. The voltage on the Red wire should cycle between 0.1 and 4.9v depending on where the mode actuator is.
6. The White wire should be at 2.5 volts when the actuator is commanded to the rest position. There will be a reading of 0 volts to command movement in one direction and a 5 volt signal to command movement in the opposite direction.

If the readings are off the harness connectors at the far right side of the dash should be check and or cleaned. Also GM has a TSB about an in line harness connector that may be the cause of your problem but I would need to know if you system has manual or auto controls before supplying that information.

Also if you do not get the full range of travel voltage on the Red wire, check to see if the slot in the shaft fully travels between the two hash marks on the actuator case. If it does not I would suspect that the actuator still may not be correctly installed.

SDixon: I will check these and get back to you. I’m sure this is kind of a stupid question but could you tell me the difference between manual or auto controls?

Sparky:

The auto system will have the word auto next to the two outer knobs. The center knob will adjust between 60 to 85 degrees.

On the manual system the center temperature knob just has the red and blue arches above the knob.

 

SDixon: Thank you. Mine is the auto system.

Sparky:

I have still been looking into your problem. In order to perform a recalibration on your 2002 Suburban with auto a/c controls you will need to either disconnect the battery or remove the Radio fuse from the underhood fuse box. Here is the procedure from GM service information.

1. Turn OFF the ignition.
2. Remove the battery positive voltage circuit fuse of the HVAC Control Module.

Important:  The scan tool must be disconnected from the vehicle to properly perform the calibration procedure. If a scan tool is connected before this procedure is completed, then new calibration values will not be stored.

Important:  Failure to wait 60 seconds will not allow the HVAC control module sufficient time to clear the old calibration values.

1. Wait 60 seconds.
2. Install the fuse.
3. Turn ON the ignition.
4. Wait 60 seconds before installing a scan tool.

I would modify this slightly by waiting 60 seconds and possibly up to 3 minutes before turning the ignition off for at least 10 seconds (no more than 30 seconds) then turning the ignition back on to check the results.

Also if you have anything connected to the vehicle that has a battery or memory circuit,  treat it as a scan tool as far as disconnecting it so it will not interfere with the process.

SDixon: Thank you.
Should the controls be set on anything specific? Can you also tell me the best method to determine whether the actuator is installed correctly?

Sparky: GM does not mention a need to preset the controls to a particular position. The ways to tell are; compare to a known good vehicle, visual inspection to check for binding during travel, look at the original actuator to see which slots were used (probably not possible in your case) and trial & error fitting.

SDixon: Thank you so much for the assistance. All voltage checked out so I pulled the actuator and cog, reinstalled both, and recalibrated. Everything works great now!

Thanks again!!!