2001 Silverado 1500 Mode Actuator Problem. Manual Controls

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#14674 Closed 2001 Chevy Silverado 1500 public

2001 Silverado 1500 Mode Actuator Problem. Manual Controls…The original mode actuator was driving to defrost and stopping in addition it would sometimes stall anywhere in its travel. . Removed and tested found potentiometer flaky, ordered AC/Delco one. I have manual controls and think I read on your site that there is no calibration. The new one is smooth during travel but will still stall at defrost. If I do not select full defrost it will go to all other settings on the selector switch. With the actuator removed I read the voltages on the new one during travel. It will travel and go to 2.5v and stop at all settings but full defrost and full floor. At full floor it will stop far from the marks on the actuator and continue to send 5v until the control is set away from full floor, it will then move and will then go to any setting. If full defrost is selected it will stop far from the marks on the actuator but will not reverse, the voltage will stay at slightly above zero volts no matter where the selector is set..
Questions are:
I have manual controls and think I read on your site that there is no calibration on this vehicle. Is that true?
When you select full defrost or full floor should the actuator drive to a predetermined feedback voltage then go to 2.5v and stop?
Does having it installed make a difference?
If so can you tell me at what feedback voltages should I read at full floor and full defrost?
I would appreciate any help Thank you.


Correct, there is not a recalibration procedure for the manual system in that year model.

Yes, it will look for  a predetermined value but it also is looking for load resistance at the ends of travel. If the actuator is not mounted that load is not recognized and the actuator will be driven to the default position which happens to be defrost.

Sorry GM does not supply that information(feedback voltages) and I have never needed to measure and record it for any repairs.

Below are a few excerpts taken from GM service information.

This line is at the beginning of every repair procedure for actuator replacement in GM service information. “Notice:  In order to avoid actuator damage, DO NOT apply power to the actuator when it is not installed in the HVAC module.” 

Mode Actuator

The mode actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer’s adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Air Distribution

The HVAC control module controls the distribution of air by the use of a defrost actuator and a mode actuator. The modes that may be selected are:

  • Defrost
  • Defog
  • Panel
  • BI-Level
  • Floor

The mode actuator is connected to the mode door by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If the HVAC control module detects a fault with the mode door the HVAC control module will try to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode door actuator. When the mode switch is placed in the defrost or defog positions the A/C is commanded on and the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all modes and recirculation is only available in the panel and bi-level modes.

Thank you for the reply. What I failed to write was that I did mount the actuator and plate first before connecting it. I drove to all positions until I selected full defrost, when I did that the actuator went to default and would not return. I then removed the actuator and plate to test it unmounted. I found with the old actuator when it goes to default that by temporarily removing the highest gear in the actuator you can spin the drive gear back to the centered position and as long as the pot gear spins with it, the actuator will work again properly when connected . I have not seen any damage to the actuator.

In testing it appears the mode control switch has 16 points of position from full defrost to full vent. With the actuator not installed, my actuator goes to 14 of the positions(from “almost” full vent to “almost” full defrost) and stops properly (2.5v on the white wire). When I select full vent with the actuator not installed it will rotate until it jams on the stops on the actuator. I have tried stopping the plate with my fingers before it reaches the stop, simulating full vent as if it was installed, but the 5v command voltage does not go to 2.5v when I do this. I have not tried simulating load at the full defrost.

Your comment “it also is looking for load resistance at the ends of travel. ” Should the command voltage go to 2.5v when I simulated load resistance by stopping the travel with my fingers? I note that GM service info you posted does not mention this load resistance.

If time permits today I will re-install the actuator and plate and measure the command voltage when the actuator stops at full vent position.
The new actuator is AcDelco 15-72505.
Again many thanks for the info and reply.


The load resistance as I called it used to be discussed in the various manufacturers service information. Basically what the logic modules look for are a stall condition within a voltage or count certain range near the known end of travel. If not you wind up with broken doors.  I have made the assumption that this information is relevant to your vehicle since it fits in with so many other GM vehicles of that era.

Thank you again for the reply. I did re-install the actuator and plate this morning. As stated in the last reply the actuator goes to 14 of the 16 positions on the selector sw. ..it stops and the command voltage is 2.5vdc. With the blower on I have verified all positions are accurate.(floor is floor, floor/vents is floor/vents ect.) ……However when full vent is selected the actuator drives the cam until the teeth on the right side white cog are fully engaged, it stops there mechanically BUT there is still 5vdc on the white wire. I did not leave it in this position for long as I fear burning the motor up. If another position is selected it moves to it. It does not jam… I did not try the full defrost as I fear it will go into default and I will have to remove and reset the actuator. If the command voltage is supposed to go to 2.5vdc when it is at the end of its travel(full vent or full defrost it’s not happening on full vent and I am scared to try full defrost.
It is usable for 14 of the 16 positions. I will leave it installed and be careful I do not go to full defrost.
If you know for certain that the command voltage is supposed to go to 2.5vdc at both ends of travel I would like to know that. If not many thanks for the info and your time.


2.5 volts on the command wire is definitely a stop/stall command. This is taken from GM service information in my first reply “When the actuator is at rest, the control circuit value is 2.5 volts. “.

Have you measured the feedback voltages at each of the 14-16 positions that you have identified? If so, did you take the measurements at the actuator harness connector, the control panel connector or both?

I will write a longer reply later but I know the feedback values are accurate as 14 of the 16 positions the actuator should go to are accurate as air blows exactly where it should at those positions. Only at the full CW(defrost only) and full CCW(dash vents only) position of the mode selector switch does the actuator fail to stop until it hits a mechanical stop.


Look forward to seeing the additional info. Thanks, Sparky

Write a reply

The ticket has been closed. If you feel that your issue has not been solved yet or something new came up in relation to this ticket, you can re-open it by clicking this link.