Check fuses
check blower motor and control module
check relay
The front blower motor power module is connected to the vehicle electrical system through a dedicated lead and connector of the front HVAC wire harness. A second connector receptacle receives the wire harness connector from the front blower motor. The front blower motor power module allows the microprocessor-based automatic temperature control (ATC) A/C-heater control to calculate and provide infinitely variable blower motor speeds based upon either manual blower switch input or the ATC programming using a pulse width modulated (PWM) circuit strategy.
The PWM voltage is applied to a comparator circuit which compares the PWM signal voltage to the front blower motor feedback voltage. The resulting output drives the power module circuitry, which provides a linear output voltage to change or maintain the desired blower speed.
The front blower motor power module is diagnosed using a DRBIII ® scan tool.
The front blower motor power module cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.
RELAY !!!
The front blower motor relay is an electromechanical switch that uses a low current input from the front control module (FCM) to control the high current output to the blower motor resistor (manual temperature control) or the blower motor power module (automatic temperature control). The movable, common feed relay contact is held against the fixed, normally closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it draws the movable common feed relay contact away from the fixed, normally closed relay contact and, holds it against the fixed, normally open relay contact. This action allows high current to flow to the blower motor.
When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, normally closed contact point. The resistor or diode is connected in parallel with the relay coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.
The blower motor relay terminals are connected to the vehicle electrical system through a receptacle in the integrated power module (IPM). The inputs and outputs of the blower motor relay include:
The common feed terminal (30) receives a battery current input from the battery through a B(+) circuit at all times. The coil ground terminal (85) receives a ground input through the front/rear blower motor relay control circuit only when the FCM electronically pulls the control circuit to ground. The coil battery terminal (86) receives a battery current input from the battery through a B(+) circuit at all times. The normally open terminal (87) provides a battery current output to the blower motor resistor (manual temperature control) or blower motor power module (automatic temperature control) through a fuse in the IPM on the fused front blower motor relay output circuit only when the blower motor relay coil is energized. The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the blower motor relay coil is de-energized.
The blower motor relay cannot be repaired and, if faulty or damaged, it must be replaced.
Oct 14, 2008 at 9:23 PM
