Control Module HVAC: Description and Operation

Fig.22 Power Module:

FRONT POWER MODULE
A blower power module is used on this model when it is equipped with the optional Automatic Temperature Control (ATC). Models equipped with the standard manual heater-A/C control use a blower motor resistor, instead of the blower power module. The blower power module is installed in a mounting hole in the evaporator housing, directly behind the glove box opening of the instrument panel. The module consists of a molded plastic mounting plate with two integral connector receptacles. Concealed behind the mounting plate within the evaporator housing is the power module electronic circuitry and a large finned, heat sink. The module mounting plate is secured with two screws to the evaporator housing and is accessed for service by rolling down the glove box from the instrument panel.

The power module heat sink will get hot when in use. Do not touch the heat sink if the blower motor has been running. The blower power module cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The blower power module is connected to the vehicle electrical system through a dedicated take out and connector of the instrument panel wire harness. A second connector receptacle receives the pigtail wire connector from the blower motor. The blower power module allows the microprocessor-based Automatic Temperature Control (ATC) heater-A/C control module 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 blower motor feedback voltage. The resulting output drives the power module circuitry, which adjusts the voltage output received from the blower motor relay to change or maintain the desired blower speed. The blower power module is diagnosed using a DRB III scan tool. Refer to the appropriate diagnostic information.

Fig.11 Power Module:

REAR POWER MODULE
A blower power module is used on this model when it is equipped with the optional Automatic Temperature Control (ATC). Models equipped with the standard manual heater-A/C control use a blower motor resistor, instead of the blower power module. The blower power module is installed in a mounting hole in the back of the rear heater-A/C unit housing, directly above the expansion valve. The module consists of a molded plastic mounting plate with two integral connector receptacles. Concealed behind the mounting plate within the evaporator housing is the power module electronic circuitry and a large finned, heat sink. The module mounting plate is secured with two screws to the rear heater-A/C unit housing and is accessed for service by removing the right quarter and D-pillar trim panels.

The power module heat sink will get hot when in use. Do not touch the heat sink if the blower motor has been running. The blower power module cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The blower power module is connected to the vehicle electrical system through a dedicated take out and connector of the rear HVAC wire harness. A second connector receptacle receives the pigtail wire connector from the blower motor. The blower power module allows the microprocessor-based Automatic Temperature Control (ATC) heater-A/C control module 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 blower motor feedback voltage. The resulting output drives the power module circuitry, which adjusts the voltage output received from the blower motor relay to change or maintain the desired blower speed. The blower power module is diagnosed using a DRB III scan tool. Refer to the appropriate diagnostic information.