The air delivery controls are divided into 7 primary areas:

HVAC Control Module

The HVAC control module (IPM) is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The dash integration module (DIM), which is the vehicle power mode master, provides a device on signal. The control module (IPM) supports the following features:

The HVAC control module (IPM) will receive information that defines the current driver of the vehicle from the driver door module (DDM) through class 2 communication. The HVAC system will memorize the following system configurations for up to two unique drivers:

This information shall be stored inside the HVAC control module (IPM) memory. When a different driver identification button is selected the HVAC control module(IPM) will recall the appropriate driver settings. When the HVAC control module (IPM) is first turned on, the last stored settings for the current driver will be activated except for the rear defrost.

Mode and Recirculation Actuators

The mode and recirculation actuators are 2-wire bi-directional electric motors. Two control circuits enable the actuators to operate. The control circuits use either a 0 or 12 volt value to co-ordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 12 volts. In order to move the actuator, the HVAC control module grounds the appropriate control circuit for the commanded direction. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.

The HVAC control module(IPM) determines the door position by counting motor pulses on one of the control circuits. These pulses are small voltage fluctuations that occur when the brush is shorted across two commutator contacts as the motor rotates. As the actuator shaft rotates, the HVAC control module(IPM) monitors the voltage drop across an internal resistance to detect the pulses. The HVAC control module(IPM) converts the pulses to counts with a range of 0-255 counts. The HVAC control module(IPM) uses a range of 0-255 counts to index the actuator position.

Auxiliary HVAC Control Module

The auxiliary HVAC control module (IPM) is a class 2 device that interfaces between the operator and the auxiliary HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The dash integration module (DIM), which is the vehicle power mode master, provides a device on signal.

Auxiliary Mode Actuator

The auxiliary mode actuator is a 3 wire bi-directional electric motor. Supply voltage, low reference and control circuits enable the actuator to operate. The control circuit uses a 0-12 volt linear ramped signal to command the actuator movement. The 0 and 12 volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

The blower motor forces air to circulate within the vehicle's interior. The vehicle operator determines the blower motor's speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. In manual operation, once a blower speed is selected, the blower speed remains constant until a new speed is selected. In automatic operation, the HVAC control module(IPM) will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

As the requested blower speed increases, the following conditions occur:

As the requested blower speed decreases, the following conditions occur:

Steering Wheel Controls

The HVAC control module(IPM) receives class 2 messages that the driver has activated a steering wheel control switch from the dash integration module. The HVAC steering wheel control button controls driver set temperature increase and driver set temperature decrease.

The HVAC system interprets the set temperature switch on the steering wheel as if the driver had activated the same switch function on the HVAC control module (IPM).

Afterblow

If the A/C compressor has been on for at least 2 minutes, the HVAC control module (IPM) will go into afterblow to remove moisture from the HVAC module. The blower motor will be activated at medium speed 45 minutes after the ignition has been turned off. The battery must have 12 volts minimum and outside temperatures must be 21°C (70°F) for higher. Afterblow air will be delivered through the last mode setting made by the vehicle operator or automatic system. The afterblow operation can be turned on with the scan tool. It is not set by the factory.

The auxiliary blower motor provides additional airflow for the back seat passengers. The auxiliary blower motor will operate as long as the HVAC control module is ON. Passengers can operate the system in both manual or automatic modes. The only time the auxiliary blower motor is not available is when the HVAC control module (IPM) is in FRONT DEFROST. The auxiliary blower motor icon will flash to indicate that the blower is not available. Power is provided to the auxiliary blower motor from the rear fuse block. Depending upon selected blower speeds, ground is either supplied directly to the blower motor or voltage is varied by a series of in-line resistors on the ground side of the circuit.

The HVAC control module(IPM) controls the mode actuator in order to distribute airflow to a desired outlet. The mode switch provides the vehicle operator with the ability to override the automatic setting. When the mode door is moved to the defrost position, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position.

The auxiliary HVAC control module controls the auxiliary mode actuator in order to distribute airflow to a desired auxiliary outlet.

The HVAC control module(IPM) controls the air intake through the recirculation actuator. Recirculation is not available when the mode is in defrost.

In automatic operation, the HVAC control module (IPM) will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation.

To place the HVAC system in automatic mode, the following is required:

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically adjust to maintain the temperature selected (except in the extreme temperature positions. The HVAC control module (IPM) performs the following functions to maintain the desired air temperature:

When the warmest position is selected in automatic operation the blower speed will increase gradually until the vehicle reaches normal operating temperature. When normal operating temperature is reached the blower will stay on high speed and the air temperature actuators will stay in the full heat position. When the coldest position is selected in automatic operation the blower will stay on high and the air temperature actuators will stay in the full cold position.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. The vehicle operator can select an extreme temperature setting but the system will not warm the vehicle any faster. In warm temperatures, the automatic HVAC system will also provide air conditioning in the most efficient manner. Selecting an extreme cool temperature will not cool the vehicle any faster.