For 1990-2009 cars

The coil side of the blower motor relay receives battery voltage through the DEF fuse when the ignition switch is in the ON position, and is permanently grounded at G201. The switch side of the blower motor relay receives battery voltage from the HTR and blower fuses at all times. When the ignition switch is in the ON position, the blower motor relay is energized and provides battery voltage to the blower motor. When the blower speed selector switch is in any position except OFF, a ground path is provided to the blower motor at G200 through the blower motor resistor (except in HIGH) and the closed contacts of the blower speed selector switch.

When the blower speed selector switch is in any position except OFF, a signal is provided to the powertrain control module (PCM) for idle control.

When the blower speed selector switch is in the LOW position, current must travel the entire length of the resistive element in the blower motor resistor before reaching ground at G200. The blower motor runs at LOW speed.

When the blower speed selector switch is in the MEDIUM 1 position, current passes only partially through the blower motor resistor before reaching G200. Because less of the blower motor resistor is a part of the circuit, the resistance in the circuit is lower, the current is higher, and the blower motor operates at a higher speed.

The MEDIUM 2 operation is identical to the MEDIUM 1 operation, except that even less of the blower motor resistor is in the circuit. The MEDIUM 2 operation is faster than the MEDIUM 1 operation.

When the blower speed selector switch is in the HIGH position, the blower motor resistor is bypassed entirely and full circuit current is applied to the blower motor.