The air delivery description and operation is divided into four areas:

HVAC Control Module

The HVAC control module is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The ignition 3 and battery positive voltage circuits provide power to the control module. The control module supports the following features:

Mode Actuator

The mode actuator is a 3 wire bi-directional electric motor. Ignition 3 voltage, ground 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. When the HVAC control module sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

Recirculation Actuator

The recirculation actuator is a 3 wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit is either grounded or opened during normal operation. If the control circuit is grounded, then the shaft rotates in the opposite direction than it would if the circuit was opened. The actuator shaft rotates until the limit is reached. If the module needs to reverse the direction of rotation, then the control circuit's state is reversed. The open circuits are held at ignition 3 voltage from the actuator. The module will maintain the control circuit's state until a new position is needed.

The HVAC control assembly applies voltage to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:

When the operator requests High speed, the HVAC control assembly applies voltage to the blower motor relay through the high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to battery positive voltage.

Off Mode

When the OFF position is selected, the HVAC control module applies voltage to the blower switch off input within the HVAC control module through the off blower motor control circuit. When the HVAC control module receives this input, any A/C request will be cancelled and the A/C request LED will turn off. Fresh air will still be brought in from the outside, but the LED indicator will not illuminate.

The HVAC control module controls the mode actuator in order to distribute airflow to a desired outlet. 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. Regardless of the mode setting, a small amount of air will be diverted to the defrost ducts to reduce windshield fogging. When the mode actuator sees an open in the control circuit, the actuator defaults to 6 volts and positions the mode door to the floor position. On startup, the HVAC control module will place the mode door in the last selected position.

The HVAC control module controls the air intake through the recirculation actuator. Recirculation is only available when the HVAC control module is in Vent or Bi-level. The operator must activate the blower for Recirculation operation. When the recirculation actuator sees an open in the control circuit, the actuator will default to the recirculation position.