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MY04 XT Auto HVAC Blower Died - Why So Complicated?

693 Views 0 Replies 1 Participant Last post by  wildlatin
I've searched and tried to absorb what posts on this subject I could find but I've found no answer...
(or I probably wouldn't be posting... duh!)

I see much about extreme frustration :mob:with the Auto HVAC 'climate control' system that is on my '04 XT but I'd be satisfied just to have a running heater blower again- I generally don't use the 'auto' mode anyway.

But after reading most of stuff here and on scoobymods I still fail to find anyone who seems to have described how the system works, and though there are tons of diagrams and discussions on the simpler blower motor + resistance network (i.e. 'manual') systems I've yet to find a description of what might be causing my problem.

Details of problem:
  • System ran fine until recently- Now, NO blower motor running on any setting (manual or auto, any speed).
  • The two 15a fuses are not blown.
  • Removed blower (with integrated circuit board... the $$$ one!:icon_eek:)
  • Power through connector to motor seems to be ~11v and varies with speed setting. (?)
  • Motor itself runs fine if after exposing circuit board, power leads directly to motor are briefly powered at 12v- motor is fine.
  • I replaced blower with same model from another vehicle- Watched it as it first it ran slowly on speed#1, I shut off, turn back on... Nothing!

IMPT: What kind of signal is sent from Auto HVAC controls to blower motor? Is it some sort of pulse-width modulation of constant voltage or ? (I didn't check voltage between all THREE wires on feed to motor... probably should have.:frown2:) Circuitry looks analog so maybe just some ratio of voltage between the 3 wires?

A decent description of how this Auto HVAC system is supposed to be controlling the speed of the blower, in conjunction with its built-in circuit board, would really help- and I've not seen a diagram or description of what it's supposed to be.
(There are many here and elsewhere about the simple motor and the resistance-based systems though.)

I did find an auto diagnostic mode for the Auto HVAC system which I am going to try tomorrow... maybe that will point to something. Has anyone used it?

I join the legions of owners who wish I just had the simple manual HVAC system instead of this overly complex system!:crazy:
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