- May 3, 2014
- 89
First, I would like to say thanks to Roadie for all the great info on Trailblazers that have helped me a lot over the last several years. I came to this site since I just learned that he came over here.
Second, I have never had a need to request help from a forum before, but I am at the end of my rope with this problem, so this is one last desperate attempt to figure this out before I break down and take the Trailblazer to the dealership.
The problem: I have a 2006 Trailblazer EXT with manual HVAC controls. The rear HVAC temperature, vent mode, and blower controls stopped working completely. The rear HVAC can be operated using the front controls, but sometimes the rear vents will not change positions when I move the vent switch, and the rear blower acts really strange. If I turn the auxiliary blower control switch on the front console to the R position to activate the rear controls, the blower shuts off and will not restart when I move the switch out of the R position. If I shut the blower off for ~20 seconds or so, then it will start back up. Also, if the rear blower is running and I move the front vent switch to the lowest position (so that the vents blow at the floor position), then the rear blower will almost always shut off off and will not restart unless I again leave it off for ~20 seconds. Sometimes, the blower will also randomly shut off without switching any of the controls and will not restart unless I shut it down and leave it off for ~20 seconds. With the blower not working and the blower speed switch on the highest setting, I checked the voltage at the blower connector and found it to be 14.4 VDC. Normally, I would replace a blower for this condition, but I read on a forum that the blower speed controller should provide a pulse-width modulated signal to the blower instead of a constant 14.4 V DC signal. Between that and the other weird symptoms, I am guessing this is probably the Auxiliary HVAC Control Module, but I want to verify this is the problem before I throw money at it.
Also, the rear temperature actuator was not working with either the front or rear controls until I disconnected the battery for a few minutes and restarted the car to allow the system to reset itself. Now, the rear temperature actuator will work with the front controls only. However, when the control switch is set to the hot position, it only blows warm and not hot air, even after I let the car run for 30 minutes.
Another thing worth mentioning is that I recently replaced the rear evaporator when I had a rear line leaking that was seized to the evaporator. The aftermarket evaporator did not have mounting holes for the torx screws that secured the blower motor speed controller to the original evaporator, but the speed controller housing was pressed into the HVAC plastic housing and stayed there without the screws, so I do think this is an issue. Also worth mentioning is that I broke the blend door shaft when I unnecessarily removed the mode actuator during the evaporator replacement. I do not think this is a problem since only the tip of the star-shaped end of the shaft broke, so the end of the broken shaft still fit inside the star-shaped insert in the mode actuator, and I super-glued the end of the shaft to make sure that it stayed there.
Has anyone had similar issues with the rear HVAC controls and blower? Is there any good way to troubleshoot this with a digital multimeter? I do not own or want to spend the money on an oscilloscope.
Second, I have never had a need to request help from a forum before, but I am at the end of my rope with this problem, so this is one last desperate attempt to figure this out before I break down and take the Trailblazer to the dealership.
The problem: I have a 2006 Trailblazer EXT with manual HVAC controls. The rear HVAC temperature, vent mode, and blower controls stopped working completely. The rear HVAC can be operated using the front controls, but sometimes the rear vents will not change positions when I move the vent switch, and the rear blower acts really strange. If I turn the auxiliary blower control switch on the front console to the R position to activate the rear controls, the blower shuts off and will not restart when I move the switch out of the R position. If I shut the blower off for ~20 seconds or so, then it will start back up. Also, if the rear blower is running and I move the front vent switch to the lowest position (so that the vents blow at the floor position), then the rear blower will almost always shut off off and will not restart unless I again leave it off for ~20 seconds. Sometimes, the blower will also randomly shut off without switching any of the controls and will not restart unless I shut it down and leave it off for ~20 seconds. With the blower not working and the blower speed switch on the highest setting, I checked the voltage at the blower connector and found it to be 14.4 VDC. Normally, I would replace a blower for this condition, but I read on a forum that the blower speed controller should provide a pulse-width modulated signal to the blower instead of a constant 14.4 V DC signal. Between that and the other weird symptoms, I am guessing this is probably the Auxiliary HVAC Control Module, but I want to verify this is the problem before I throw money at it.
Also, the rear temperature actuator was not working with either the front or rear controls until I disconnected the battery for a few minutes and restarted the car to allow the system to reset itself. Now, the rear temperature actuator will work with the front controls only. However, when the control switch is set to the hot position, it only blows warm and not hot air, even after I let the car run for 30 minutes.
Another thing worth mentioning is that I recently replaced the rear evaporator when I had a rear line leaking that was seized to the evaporator. The aftermarket evaporator did not have mounting holes for the torx screws that secured the blower motor speed controller to the original evaporator, but the speed controller housing was pressed into the HVAC plastic housing and stayed there without the screws, so I do think this is an issue. Also worth mentioning is that I broke the blend door shaft when I unnecessarily removed the mode actuator during the evaporator replacement. I do not think this is a problem since only the tip of the star-shaped end of the shaft broke, so the end of the broken shaft still fit inside the star-shaped insert in the mode actuator, and I super-glued the end of the shaft to make sure that it stayed there.
Has anyone had similar issues with the rear HVAC controls and blower? Is there any good way to troubleshoot this with a digital multimeter? I do not own or want to spend the money on an oscilloscope.