Community Member Credit: Sparky
This 2003 Nissan Maxima came in with the complaint that only the highest blower speed was working. The air would not blow at all, on the lower speeds. Suspecting a faulty blower resistor, I went to the passenger side of the dash.
The blower resistor is located near the firewall under the passenger side of the dash. It is the piece that the connector with blue wires is attached to.
Two phillip’s headed screws hold the resistor to the blower housing.
To release the locking tab, it needs to be pushed in where I am pointing at with my pocket screwdriver.
If you want to test the system this is what you will need to know.
The blower resistor and blower switch are on the ground side of the blower motor circuit.
With the resistor harness disconnected and the ignition on, there will be bleed through battery voltage on the larger blue/white wire. In the blower switch position 4 or high the blower switch directly connects this wire to chassis ground and the highest blower speed is achieved.
When the blower speed is set to the 3 position the ground is sent from the blower switch to the resistor on the blue/red wire. It passes through one resistor and the speed is reduced slightly.
When blower speed 2 is selected the ground again is sent form the blower switch to the resistor but this time it is sent on the blue/yellow wire. At the resistor is passes through two resistors and the speed is dropped even further.
When blower speed 1 is selected the ground signal again is sent from the blower switch to the blower resistor and this time it is on the blue/black wire. At the resistor is passes through three resistors and the lowest blower speed is achieved.
If there is no bleed through voltage at the blue/white wire you will need to see if there is power on the white/blue wire at the blower motor itself.
If voltage is not present on the white/blue wire at the blower motor you will need to check the fuses and relay. If power is present the blower motor is faulty.
I also wound up checking and changing a restricted cabin air filter in this vehicle. It is likely that the dirty filter contributed to the resistor failure.