How to fix a problem Blower Motor on Honda
The blower motor circuitry in Hondas is much different than the traditional switch/resistor setup found in other vehicles. Power flows to a blower motor relay first. When you turn the key to on the relay provides power directly to the blower motor. Switch the fan on tells the heater control unit to send a pulsed voltage signal to the power transistor. By pulsing the transistor, the control unit is literally switching the blower motor ground connection on and off several times per second to control fan speed. This setup completely eliminates the need for a resistor and all the wasted energy the resistor consumes.
To get a real good idea whether the problem is the control unit or the power transistor, you need a scope. There is a procedure to test the power transistor with an incandescent test light by removing the blue/yellow wire from the connector to the power transistor. Then connect the ground clip of the test light to battery +voltage and quickly touch the probe to the terminal on the power transistor where the blue/yellow wire used to attach. If the blower motor starts, the power transistor is OK. If not, replace the transistor.
FYI, shops report that the power transistor is usually the cause of the problem when a blower motor fails to run. The part is only available from Honda (that I know of) and costs about $25.
If the power transistor is dead, it may also cause the A/C to not operate. So if you have both problems, fix the blower motor problem first before moving on to the A/C issue.
© 2012 Rick Muscoplat
Posted on by Rick Muscoplat