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.
The biggest thing to not overlook is that there are controls on the Rear Seat Audio (RSA) controls for the rear passengers to control HVAC functions. Check the positions of those switches. Testing at the rear temp actuator is a s follows.
The yellow wire is system ground.
The brown wire is ignition power.
The gray wire is a 5 volt reference wire.
The white/black wire is the control wire. There should be a reading of 0, 2.5 or 5 volts present. The 2.5 volt reading is a stall command. The other two are for direction.
The dark blue wire is the position sensor output from the actuator to the control assembly. It will vary from a nominal 0 volts to a nominal 5 volt signal as the actuator moves.
Sparky, I assume it has electronic controls. It is a loaded Z71 with all the bells and whistles. It has automatic temp control. I replaced the rear control module tried several “reset” techniques. The temp actuator goes to the bottom then passes past the top “tic” on the actuator and stops. Switched the actuators, same result. Starting to think the door flap is flexing but I thought this “new” module was supposed to preclude overtravel.
I need to know if your Tahoe has auto or manual controls?
Sparky, enjoyed your posts! I too have a problem I didn’t see here. 2004 Tahoe ZR1. Rear heater actuator goes to park. The upper/lower works fine. Switched the two and the heater actuator works on the up/down and up/down parked. Replaced control module and no change….Wires seem to have varying voltage based on moving settings. Stumped!
Hi Roland,
I am assuming that you have two problems. The rear a/c does not get cold and that is associated with a clicking noise coming from the rear of the vehicle. That will likely be a faulty rear blend door actuator. You will need to remove the passenger rear panels to get to the actuator.
The other issue you mention was that the a/c would start blowing hot after encountering a big bump in the road. I am again assuming that you are referring to the front driver’s side vent temperature. If so two things are likely. There could be a poor connection at the passenger side junction block connectors. Remove the passenger side dash end cap. Disconnect and reconnect the harness connectors several times. Inspect the terminals for corrosion or any other damage. Correct any issues found. If that does not clear it up the next likely issue would be a faulty driver’s temperature door actuator.