This 2003 Chevrolet Silverado came in with the complaint that the passenger vents were stuck on heat at the end of August in South Carolina.. Since it was late I decided to try a procedure that GM came out with several years ago. It applies to actuators that have over traveled for one reason or another. The following is an excerpt from the GM bulletin.
A replacement HVAC actuator is inoperative or has worked one time and quit.
The HVAC control head learns the stopping points based on how far the HVAC DOOR travels. If it reaches the mechanical stops on the back of the actuator, it will be outside the range that the HVAC control head can learn. If the actuator was not mounted to the HVAC case prior to plugging in it’s connector, the actuator will go out of range and will be inoperative.
Always attach the HVAC actuator to the case before installing the electrical connector.
If an actuator is out of range, it may be possible to bring it back into range by following the procedure below:
- Turn ON the ignition with the engine OFF.
- Connect a 3 amp fused jumper wire between the actuator control circuit and the 5 volt reference circuit of the actuator connector.
- Remove the jumper wire and actuator connector when the actuator is at the center position.
- If the actuator doesn’t move in step 2, try installing the jumper wire from control circuit and the ground circuit of the actuator.
- With the actuator in the center position, install the actuator to the HVAC case and secure the mounting screws and then connect the actuator connector.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.”
The above information seems to have been provided by GM mainly to combat actuators being stuck when the harness is connected and the actuator is not attached to the HVAC box and thus being returned as defective. That is all fine and dandy but we can use this information to un stick and actuator that has over traveled due to other causes. Mainly, there has been a problem with over travel caused by compression of the foam sealing layer on the actuator doors themselves coupled with loose software parameters that did not originally take this into consideration. Also we can use this information to add to diagnostic routine that may not include the use of a scan tool capable of interacting with the HVAC system.
The first thing that I had to do was to make a workable fused jumper wire with a 3 amp fuse. The next picture is what I came up with. I used a set of multimeter leads and a fused jumper wire together. The multimeter leads gave me the contact point that I needed, which was a solid piece (no frayed wire ends that could possibly bridge multiple circuits) and that was long enough to back probe the junction block harness in a comfortable manner.
I used an ATO style fused jumper wire. Made from an inline fuse holder.
I had attached small blade terminals to the in line fuse holder to make it a fused jumper wire. I inserted the blade terminal into the cross pattern in the meter end of the test leads. Together I have a very functional fuses jumper wire.
Now, the test point. The most practical point to do this test and more is at the passenger side junction block that is located under the cover located at (you guessed it) the passenger side of the dash.
I backprobed the white/black wire slot of the C8 connector, pin E with one lead of my 3 amp fused jumper wire. The C8 Conneector is the gray upper middle connector as shown in the next picture. Please click on the following pictures to enlarge them for a better view.
Pin designations of the C8 connector as viewed from the wire side of the connector.
“A” White/Black, Lower left corner, Lower left air duct temperature sensor with auto controls.
“B” Brown (2), Left side middle, Ignition “3” voltage for the left & right air temperature actuators.
“C” Brown (2), Left upper corner, Ignition “3” voltage for the mode
& recirculation actuators.
“D” Dark Blue, Upper Right Corner, Passenger side air temperature door
POSITION signal with auto controls.
“E” White/Black, Right Side Middle, Passenger side air temperature door CONTROL signal with auto controls.
“F” Dark Green, Lower Right Corner, Recirculation door CONTROL signal.
With the other end of my 3 amp fused jumper wire, I backprobed the light blue/black wire of the C4 connector pin “H” for one direction of travel. For the opposite direction of travel I connected to the “M” pin. Sorry at this point I do not remember which one moved a particular direction. The C4 connector is the large brown connector in the upper left corner of the junction block as seen in the next picture. Please click on the picture to enlarge for a better view. It did free the stuck actuator and I was able to disconnect the actuator harness to prevent anymore unwanted heat. The vehicle will still need an new actuator as the old one is actually faulty. Although I used a Tech2 scan tool to determine the actuator was faulty, the same can be done by monitoring the voltages on the command (control signal) and the actual position (position signal) of the affected actuator. We would be looking for a smooth voltage change on the position signal as the actuator is commanded to move. It should range from a nominal 0 volts to a nominal 5 volts. The range will be smaller than this but I am trying to get this post completed and will update it later with more specifics. The command or control signal should be either 0, 2.5 or 5 volts. 0 volts is a command to travel on one direction. 2.5 volts is a stop command. 5 volts is a command to travel in the opposite direction of 0 volts.
Pin designations of the C4 connector as viewed from the wire side of the connector.
“A” Black, Lower left corner, Ground
“B” Gray/Black, Left side middle, Lower right air duct temperature sensor signal with auto controls or Orange, Left side middle, Blower motor high control (C42)
“C” Brown(2), Left upper corner, Low reference (internal ground) lower left and right air temperature sensors with auto controls or Purple, Left upper corner, Medium “3” blower motor control (C42).
“D” Red, Lower 2nd left, Battery positive voltage.
“E” Purple, Middle 2nd left, Recirculation door POSITION signal with
auto controls or Tan, Middle 2nd left, Blower motor medium “1” control (C42) RPO code.
“F” Purple/White, Upper 2nd left, Blower control with auto controls.
“G” Yellow, Lower 3rd left, Blower motor low control with Manual controls.
“H” Light Blue/Black (2), Middle 3rd left, 5 volt REFERENCE right and
left air temperature actuators.
“I” Not used as it is easy confused with the number 1
“J” Light Blue/Black(2), Upper 3rd left, 5 volt REFERENCE mode and
“K” Light Blue, Lower right corner, Medium “2” blower control (C42)
“L” Yellow(2), Middle right, Low reference internal ground)
recirculation and mode actuators.
“M” Yellow(2), Upper right, Low reference (internal ground)
right and left temperature actuators.
I did not need the following information for my situation but I decided to go ahead and post it as it may help others.
Pin designations of the C5 connector as viewed from the wire side of the connector.
“A” Blank, Lower left corner, Not used.
“B” Light Green, Middle left side, Mode door POSITION signal.
“C” Tan, Upper left corner, Mode door CONTROL signal.
“D” Dark Blue, Upper right corner, Left air temperature door
“E” Light Blue, Middle right side, Left air temperature door
“F” Blank, Lower right corner, Not used.
The remaining connectors do not have any circuits related to the HVAC system.