Air Speed

The blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed by toggling the blower motor switch manually or by using the automatic mode. The blower motor will only operate if the HVAC control module is in any position other than OFF, and the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module.

Power is provided to the blower motor from the blower motor control processor through the blower motor supply voltage circuit. The blower motor control processor receives power from the fuse block through the battery positive voltage circuit. Ground is provided by the blower motor control processor and ground circuit.

The HVAC control module receives power from the fuse block on the ignition 3 voltage circuit along with the battery positive voltage circuit. The module is grounded by the ground circuit. The HVAC control module communicates directly to the Powertrain Control Module (PCM) on the HVAC class 2 serial data circuit, through a splice pack, and through the PCM class 2 serial data circuit.

When any blower speed is selected, whether manual or automatic, the blower motor control processor will control blower motor speeds based on voltage signals from the HVAC control module. A 5 volt signal is sent from the blower motor control processor to the HVAC control module on the blower motor speed control circuit. When the driver manually selects a blower speed or the automatic HVAC system determines a needed speed, the HVAC control module will provide a Pulse Width Modulated (PWM) ground. The remaining voltage at the blower motor control processor is used to provide a blower motor speed signal. A 12 volt signal is sent to the blower motor from the blower motor control processor on the blower motor supply voltage circuit. The blower motor control processor varies the ground on the blower motor control circuit internally with a separate PWM signal. An open circuit, short to ground or short to battery on the blower motor speed control circuit will disrupt the PWM signal and cause the blower motor to not operate. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

When in manual mode, the driver can change the blower speed by toggling the FAN switch. If the driver toggles the FAN switch once, the blower speed will increase/decrease 1 level. Holding the FAN switch will increase/decrease the blower speed to the maximum/minimum speed.

Recirculation Mode
When the Recirculation Mode (RECIRC) is requested, whether manual or automatic, a solenoid inside the vacuum control assembly connects the recirculation actuator to the vacuum source. Power is provided to the recirculation solenoid by the ignition 3 voltage circuit. Ground is provided by the recirculation mode valve solenoid control circuit and HVAC control module. When the solenoid is grounded, vacuum is supplied to the recirculation actuator. The recirculation actuator retracts, closing the recirculation door. This draws air from inside the vehicle instead of fresh air from the outside. The recirculation mode can be used in both automatic and manual operation. The only time recirculation is not available is when FRONT DEFROST is selected. Recirculation is allowed in MIX-BLEND mode when the A/C compressor is on. If the recirculation switch is pressed and recirculation is not available, the RECIRC LED will light for one second and then go off to alert the driver that recirculation mode is not available. When in automatic mode, recirculation will stay on until either the vehicle operator selects outside air or the automatic system has cooled the vehicle sufficiently.

Automatic Modes
The automatic HVAC system will warm up/cool down and maintain the interior temperature of the vehicle by controlling the A/C compressor clutch, blower motor, air temperature, mode and recirculation actuators to achieve the desired temperature. Blower speeds will change automatically based on inputs to the HVAC control module. The HVAC control module will always come back to the last settings after an ignition cycle or, if equipped, to the last settings of the driver by pressing the UNLOCK button on the remote keyless entry fob and placing the ignition in RUN.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. On cold engine start-up, the blower motor will start out at low speed and will increase speeds as engine coolant temperature increases. To warm the interior quickly, maximum heat mode is used where the blower is at maximum speed, floor mode, air temperature is in full hot and outside air is being drawn in. The vehicle operator can select the extreme warm setting of 32°C (90°F), but the system will not warm the vehicle any faster. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

Setting the temperature to 32°C (90°F) will lock the HVAC control module in maximum speed, floor mode, air temperature in full hot and outside air is being drawn in. The AUTO LED will not illuminate at this extreme temperature setting. The HVAC control module will not control the HVAC system automatically until the set temperature is lowered from 32°C (90°F). Once the temperature setting is lowered, the AUTO switch will have to be pressed again to activate the automatic HVAC system. The AUTO LED will then illuminate.

In warm temperatures, the automatic HVAC system will provide A/C in the most efficient manner. On initial engine start-up, the blower motor will come on at low blower speeds to purge the HVAC module of moisture. To cool the interior quickly, maximum cool mode is used where the blower is at maximum speed, vent mode, air temperature actuator is in full cold and the recirculation actuator is drawing air from inside the vehicle. The vehicle operator can select the extreme cool setting of 16°C (60°F), but the system will not cool the vehicle any faster. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

Setting the temperature to 16°C (60°F) will lock the HVAC control module in maximum speed, vent mode, air temperature in full cold and recirculation mode. The AUTO LED will not illuminate at this extreme temperature setting. The HVAC control module will not control the HVAC system automatically until the set temperature is raised from 16°C (60°F). Once the temperature setting is raised, the AUTO switch will have to be pressed again to activate the automatic HVAC system. The AUTO LED will then illuminate.

VF Display
When you start the vehicle, the display will show the current fan speed, mode and driver side set temperature for a few seconds and then show the outside air temperature. After a set temperature change is made, the new set temperature reading will be displayed for a few seconds & then go back to outside air temperature. When the HVAC control module is off, only the outside air temperature will be displayed.

When the HVAC system is in full automatic mode, the word AUTO will appear on the display. If you have selected a manual fan speed, then the fan symbol will appear on the display If a manual mode has been selected, the corresponding mode symbol will appear on the display.