This 2003 GMC Envoy came in with the complaint that the a/c will only blow out the defrost and floor. Not through the dash vents. I checked codes and found a code B0263 for a fault with the mode actuator. I first ran into this problem after changing a battery in one of these vehicles last year. Whenever the battery is disconnected the HVAC unit will perform a recalibration of all doors. This causes the door motors to be moved full cycle and the mode door will stick some times. I now hook a jump box to the system before changing the battery in Trailblazers or Envoys to prevent a recalibration from occurring. This way I will not be blamed for a stuck actuator motor.
Anyways to change the actuator motor, first drop the hush panel under the driver’s side of the dash. There are some parts that have to be disconnected from the panel including the turn signal flasher assembly shown in the next picture.
Next, I removed the lower dash knee panel to have a little more room to work.
I had to pull a push pin retainer out at the left side of the duct work in order to remove the driver’s floor vent.
Now, I could finally see the actuator on the side of the heater a/c box.
I removed the actuator and installed the new one. Performed a recalibration with my Tech 2 and put all the panels back in place. A recalibration can be done by disconnecting the battery for at least one minute, reconnect the battery, start the engine and leave the a/c controls alone. I would recommend letting the engine run for at least two minutes, turn the ignition off for at least ten seconds but no more than thirty seconds and then restart the engine so that confirmation of the repair can be done.
I do not recommend connecting the wiring to the actuator until it is installed. They come prepositioned for easier installation.
The notch at the lower edge of the gear is an alignment point. There is a corresponding tab on the door linkage that needs to be lined up with this notch.
To purchase the mode valve actuator, please click here. To see updated information about actuator positions and alignment, please click here.
Hi Jen,
Start by checking the fuses under the hood and under the back seat. If all the fuses are okay, make sure the ignition is off. Disconnect the battery cable and depress the brake pedal for one minute. Connect the battery cable and start the engine. Hopefully the a/c panel will light up. Do Not touch the a/c controls. Let the engine run for four minutes. Switch the ignition off for at least 10 seconds but no more than 30. Restart the engine and check the a/c controls.
I have a 2004 trailblazer that i was having a bad misfire on and then was idling very rough. I took it to advanced auot and they ran codes that said the cylinder 3 had a bad misfire and that the ect sensor needed changed. I replace the coil in cylinder 3 and replaced the ect sensor. The misfire went away after changing these parts. Drove the vehicle for 50 miles and the rough idle and misfire came back. TOok the vehicle back to advanced and it was reading codes for a cylinder 1 misfire and bad coil. Replaced that coil and still same problem. THey also tested the battery there and it needed changed. Changed the battery and now the dual automatic control system will not turn on at all. NOthing comes on the screen if you press buttons. THere is some hot air blowing out of the front vents. Any advice on what to check? Thanks in advance!
-Jen.
Well, eventhough I was concerned that implementing the calibration process could produce the same sticking problem that disconnecting the battery created in the first place, I proceeded with your instructions. Lo and behold, the a/c mode now works perfectly!!! Thanks for the exceptional web site.
I can understand your confusion. Just remember that you are replacing a worn part. The wear in combination with a recalibration is what causes the old actuator to get stuck. the new part will not do this when installed. Years down the road it may happen again when the battery is disconnected. The trick on these and a lot of vehicles is to install a backup battery in the system whenever the battery has to be disconnected. Keeping the battery circuit in tack prevents the recalibration from happening automatically.
I have a 2004 GMC Envoy, purchased the new mode actuator, but re-read the calibration instructions and am still confused…if I install the new actuator and then disconnect the battery to “recalibrate” don’t I risk having the new actuator stick just like the old one did when I replaced the battery?