Chart 1C-1 Blower Motor Will Not Run In Any Mode

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

Blower motor speed is determined by the amount of voltage applied to the motor. This voltage varies from approximately 4 volts (low speed) to approximately 12 volts (high speed).

The speed at which the blower motor operates is governed by the H-A/C control. The blower motor speed can be adjusted manually by pressing the blower control "UP" or "DOWN" switches or automatically by placing the H-A/C control in the "AUTO" mode.

The H-A/C control sends blower request information to the blower motor control module in the form of a variable voltage signal. This voltage signal ranges from approximately 2.5 volts, for minimum blower motor speed, to approximately 7 volts, for maximum blower motor speed. An amplifier and driver circuit in the blower motor control module supplies between 4 and 12 volts to the blower motor according to the request signal from the H-A/C control. Blower motor voltage is also sent back to the H-A/C control to insure blower speed stability and the indicate any failure in the blower motor circuitry.

DIAGNOSTIC AIDS

1. Check for an open in I/P fuse 38. If open, repair short to ground in CKT 940.

2. Make sure grounds G200 and G202 are clean and tight.

3. If blower motor can be controlled in either the manual mode or the auto mode but not in both, replace the H-A/C control.