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02 trailblazer, at one point the heat/ac would only work on level 4. Now both selections barley blow from the vents. (There's no noise when switching to different levels)


   
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if all the lower speeds are not working and only high works I would look at the blower resistor. All the lower speeds go through the resistor. High speed bypasses the resistors and is full battery voltage through the relay in the resistor assembly. Now, after that, when no speeds work I would look at the the fuses and the signal to the blower motor. You can unplug the blower motor and put a test light between the two contacts in the harness connector. turn on the fan and see if the light lights up in any of the speeds. If it does light up in any position plug the fan back on and see if the fan runs. If you don't have the test light light up in any speed check the HVAC fuse #44, a 30 amp fuse. #38 and #39 10 amp fuses. All in the rear fuse block. Then there is a blower fuse 40 amp fuse #35 in the underhood fuse block for high speed. (power for the high speed relay)

When the blower motor gets old it may draw more amps. Taking out fuses, relays and switches.


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File comment: Chevy Trailblazer HVAC blower motor wiring schematic.
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abs011188 wrote:
02 trailblazer, at one point the heat/ac would only work on level 4. Now both selections barley blow from the vents. (There's no noise when switching to different levels)

Also see this link for Trailblazer Blower Resistor Wiring. A pic at the bottom of page.
Also, Chevy Trailblazer Mode Actuator.


   
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02 trailblazer, at one point the heat/ac would only work on level 4. Now both selections barley blow from the vents. (There's no noise when switching to different levels)..I did forget to mention that on the drivers side when on the heat selection, the passenger side always blew cold.


   
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you have more than one problem now. you will probably have to trace down the whole network. temperature is controlled with blend doors that work on actuator motors. you will have to check if the actuators are bad or the controls are bad. Scan cor codes an see what codes the hvac module has in it. fans that only work on high is usually a sign of a blower resistor or fan module. Temperature or mode is hvac module or actuator motors. Fans that don't work at any speed is blower motor or fuse/relay.

If you don't know a lot about the electrical system for the HVAC you may have to take it to a shop that can go through and check it all out. I sent the diagram for the blower motor but the blend and mode doors is more complicated.

did you do any of the checks that I wrote you about?


   
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I did make another look over(on my trailblazer), and over the different message boards. I did hear a buzzing noise switching from level 3 to 4.. with no heat/ac blowing from any of the vents including the defrosting mode. (at one point the drivers side would blow heat while the passenger side did not - but the ac would work on all sides but only on level 4 for both heat and a/c, now nothing.) I don't know if this has anything to do with my problem but I didn't start experiencing this problem til' after I had my power steering column replaced..


   
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you need to do some testing to find out what is going on. there is no substitution for diagnostic testing. unless you want to just start replacing parts. what have you tested so far? Have you scanned the HVAC? Tested the blower motor? Checked the fuses? door actuators? heater controls?

without finding out what is wrong how could someone know if it's related to the steering column work you had done? I have come to realize that many strange things have been found when working on cars. Things that seem totally unrelated have been tied together when electricity looks for a ground.


   
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