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 clutch hub did not lock in when the relay was bypassed.
You would have to visually check to see if the clutch hub locks in when the relay is bypassed. If you do not see any problems, I will need to know the current system pressure and the outside temperature.
Before the AC started blowing hot air, I had checked the charge, and it was around 42psi. When I bypassed the relay I connected 30 to 87 with a piece of copper wire. I used a volt meter and there was 12v passing through the wire. How would I check to see if the clutch was energized? It did not kick on. I will check the compressor belt this evening.
May seem dumb but I have to ask to get them out of the way. Have you checked the compressor belt to make sure it is installed and good? Have you check the refrigerant charge? When “bypassing the relay”, which terminals were connected and did you check to see if the clutch had been energized?
I have a 2003 chevy Tahoe. I recently replaced the blower motor resistor. Now that all 5 speeds are working, my A/C started blowing hot air. My compressor will not engage, and I have bypassed the relay, as well as replaced the relay with a working one. Nothing has worked. I tried to bypass the low pressure switch, and it still did not come on. Before the AC started blowing hot air, it would work and blow cold most of the time, and then it would blow humid air, with a white mist coming from the air vents. I would turn off the A/C and it would work again after the system was off for a while. Usually after I turned the car off, and back on. I am at a loss, please help…It is hot in Houston in the summer time…