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Q: Blower Motor works on High Speed only on 2000 Honda Civic

My Heater Blower Motor only works on high speed. I've already changed the resistor, blower motor, blower motor relay & finally the control switch. I'm still in the same position as before. I need some help. I'm about to bring the car to the dealer. Thoughts???
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The power transistor controls the motor speed and it is shorted causing the blower to run high all the time. Desolder the power transistor and with diode check, check the base-emitter and base collector junctions. You will probably find a collector emitter short.
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The blower motor relay is needed to supply power to the blower motor, the fuses #55 and #17 must be OK if you have high speed operation. You would need a wiring diagram and acess to the wires at the back of the heater control panel to check its operation, but if you have good fuse/power at fuse #17 and #47 there is a separate "power transistor" behind the glove box (on the heater box) 3 wire : blue/black 12v ignition key on, black is constant ground, light green/black is controlled by the heater controls. Check this as best you can but I hate replacing components with out using a factory wiring diagram and testing components to find a failed component.
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It sounds like you've checked everything. Have you the wiring diagram for the Honda and make one more pass through the circuits. It looks pretty simple, the heater control unit is the one that is hardest to test the rest are just power, ground, and switches, I can't see what we could be missing.
I've already checked the continuity of the wires from the transistor to the blower motor. What else is there?
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