This 2004 Chevrolet Tahoe came in with the complaint that the air on the driver’s side would change from cold to hot while driving down the road. When it shifted to hot the customer could not get it to turn back cold. Sounds like a faulty air mix actuator to me. I checked codes and sure enough there was a code B0408 for the left air temperature actuator. I checked the commanded position versus the actual position and there was a large difference in the counts. This is only important if you have a scan tool that will access this system. There are other tricks that can be used to test that I will show later. The driver’s or left air mix actuator is located on the lower passenger side of the dash. If present the hush panel has to be removed. This one is easy because there is no floor mounted center console. If you have a floor console please see the information at this link to see how to deal with one screw.
I removed the four 7 mm headed screws and pulled the panel out of the way.
I knew I was changing the actuator, so I disconnected the wiring harness connector and removed the two 5.5 mm headed screws
Then the actuator simply pulls down. There may be some resistance if the actuator is at the full stop position.
Slide the new actuator into position, install the mounting screws and reconnect the wires. After this was done I recalibrated the actuator with my Tech 2 scan tool. If you do not have a scan tool you may disconnect the battery for one minute. Reconnect the battery and start the engine. The key point is DO NOT TOUCH the a/c controls for at least one full minute. Actually, I prefer to wait 4 minutes because I remember reading that a few years ago and the extra time does not hurt anything. After one full minute turn the ignition off. Restart the engine and check the door operation.
Proper operation can be seen in the data stream in that the commanded and actual positions are at nearly identical counts.
To do testing with a voltmeter at the harness connector you will need to test the following. Check for ignition power on the brown wire. If power is not present check the HVAC 1 fuse in the left interior fuse box. Check for a 5 volt reference signal on the light blue/black wire. All of the next tests must be done with the harness connector plugged into the actuator. The yellow wire is a low reference wire from the control head (ground, internal system not chassis). The light blue wire is the position signal wire from the actuator to the control head. If the actuator will move the voltage will change up or down depending on the movement of the actuator (between 0 and 5 volts). The dark blue wire will have basically three different voltages that are important. 5 volts is a signal to increase the door position, 0 volts is a signal to decrease the door position and 2.5 volts is a signal to hold the door position. So with that information turn the ignition on and touch the black lead of your voltmeter to the yellow wire. Touch the red lead of your meter to the brown wire and check for a reading of battery voltage. Next touch the red lead to the dark blue wire and check for either 0, 2.5 or 5 volts depending on command. You will probably need an assistant to adjust the temperature control for the driver’s side.
Something else you need to know. If you buy a new actuator make sure the part numbers match. At the time of this writing the aftermarket (non dealer) application books are incorrect. You have to buy an actuator for the passenger side to get the correct actuator for the driver’s side. Crazy but true. I cannot think of the number of actuators I have changed that have already been replaced by others. If you install the wrong actuator, it will rotate to a full stop and never move again.
This is the box that the actuator I installed came in and the numbers on the actual parts matched (52402588). The short number is 15-72971. Long number 89018365 and it is listed as the passenger or top air mix actuator. To order this part please click here.
Hi Sparky, thanks for sharing your time and knowledge.
I have a 2001 Chev Silverado. When heating control is in the defrost position the air intake indicator goes to outside air and only cold air blows. If the control is set to dash or floor the indicator goes to recycled air and it blows warmish, not hot.
You have explained things very well but I’m afraid I still can’t figure what solution applies to my situation. I live in a small town and haven’t been able to get the truck into a mechanic and it’s near undrivable now. Appreciate any further advice you can offer!
At this point I would advise having the HVAC codes and data checked. Also see if your truck has the most current software updates. Some other possibilities to check for are a physically damaged door, faulty control head assembly and fretted/corroded terminals at the passenger side junction block.
Yes, I used a GM/AC Delco actuator. Part # 89018365. It worked fine for a couple of days after I replaced it, but then started the intermittent knocking again. Would not calibrating is properly after replacement cause this? No teeth are damaged on the actuator that I removed, and it’s still making the same sound so I’m assuming the teeth on the next actuator gears are okay also.
Did you use a Delco brand actuator, what part number? I recently did a post (Nov 15, 2011) about a ticking/ clicking noise in an Impala that was caused by two or three missing teeth on an internal gear. The noise was quite loud.
It’s from the actuator on the passenger side at the top, and adjusting the temperature cooler makes the ticking stop. I don’t have any codes as I don’t have access to a scan tool. I did the recalibration as advised by a friend at a GM dealer. He didn’t give me the correct procedure. Since then I’ve recalibrated it several times and it seems to work for a short while and then starts making noise again. It will make 2-3 clunks when turned to the hot position every time as well. Thanks for your input. =)