AC Delco HVAC Door Actuator
Operation and Calibration

Long gone are the cables and rods jutting out of the firewall
to operate the heater control valve or a vacuum unit pulling a
blend door open.  These days it’s electrically driven actuator
motors (modules) that accomplish the job.  There are several
different types of modules used in today’s GM cars.  They
all function in different ways but accomplish the same end
results. Even though this article pertains to GM products much
of the same operation features are very similar to other
manufacturers as well.  Understanding the basic fundamentals
of the different types of modules used is essential in proper
diagnosing. Hopefully, this will give you a better idea of what is
going on when those stubborn doors fail to move. 

Two Wire Actuator:  The two wire actuator is the simplest of them all.  Generally an 8 to 12volt signal provides the needed voltage and ground from the control head to the actuator motor.  A common use would be for a door that only uses two positions such as a recirculation door where it is either fully open or fully closed.  The HVAC control head uses its pre-programmed logic and actuator endpoints to position the door correctly.  A trouble code may set if the components start to wear and the endpoints drift too far from the pre-programmed positions.  Most of these endpoints are calibrated during the relearn procedure.

Three Wire Actuator: The three wire has the same type of power and ground leads and one extra lead which is an input wire from the HVAC control head.  These three wire actuators use a preprogrammed logic chip containing the necessary program information to run the actuator in the required position. As the temperature lever is changed the internal potentiometer inside the HVAC control head sends the appropriate voltage to the actuator, now the potentiometer in the actuator compares its internal circuit voltage to the signal from the control head, and when the two match the circuit voltage is turned off to the motor.

Five Wire Actuator: The five wire or “tri-state” actuator uses three of the five wires as a feedback potentiometer circuit. The other two wires are for ignition voltage and control head signals. Once the signal is received from the control head the logic circuit inside the actuator uses its bidirectional electric motor to move the door to the appropriate position.  When a zero voltage is applied to the circuit the motor rotates in one direction.  When 5 volts is applied to the same circuit the motor rotates in the opposite direction. If say, 2.5volts is applied the motor will stop rotating.  This design has sliders moving on resistive paint strips while the previous two actuators have potentiometers. 
The HVAC control head expects to see the actuator move to a certain position with the given signal provided, if the door gets outside of that preprogrammed position the controller becomes confused and attempts to try and find the correct position by continually searching for it or will stop once it reaches its default position.  Sometimes this is associated with a ticking sound created when it is trying to find the correct position. (Not to be confused with the ticking sound from a broken plastic gear inside the module.)
If you remove the fuse for a minute or so the existing information the control head has in its memory will be erased.  Then the control head will have to go into its relearn procedure to locate the door positions.
DTC’s B0229, B0414, B0424, and B3770 may set as a result of the door not finding the correct position.  A control head reflash may be necessary to expand the acceptable range from 5-250 counts to 0-255 counts which will allow for a little extra room for the door and the controller to react. If for some reason a door is jammed the reflash changes the “hold” or crush time from 2 seconds to 0.4 seconds.  These changes should eliminate the clicking sound from the door traveling to its farthest limits.

Bi-Directional Actuator: These are five wire actuators as well and perform the same way as the five wire does.  Three wires are for the potentiometer feedback while the remaining two are the positive and negative circuits used to drive the actuator motor.  These circuits run from the control head and drive motor based on the selections made by the operator.

Recalibration Methods
Recalibration without a scanner
Do not adjust or move any of the positions while the HVAC control head is performing its self-calibration.
1.Ignition Off
2.Install new control head
3.Start vehicle
4.Wait 40 seconds for the control head to self-calibrate.
5.Verify that there is no DTC’s stored.

Recalibrating with scanner
1.Clear all DTC’s
2.Ignition off
3.Install new control head
4.Start vehicle
5.Initiate the “motor-recalibration” feature found in the heating and air conditioning special function menu (Tech II)
6.When completed check for any DTC’s

Alternative Method
1.Clear DTC’s
2.Ignition off
3.Install HVAC head
4.Remove HVAC fuse for 10 seconds
5.Reinstall fuse
6.Start vehicle
7.Allow HVAC to perform self-calibration
8.Verify no DTC’s are present

Understanding any system before attempting to repair any part of it is always more beneficial to not only the mechanic/technician but for the customer as well.  And, it sure sounds a lot better when a technician can explain how something works in a customer’s car rather than just replacing a part because the scanner or code said that’s what to do.  You’ll gain not only respect from the customer but more than likely a lifelong one as well.

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