The air delivery description and operation is divided into 4 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 battery positive and ignition 3 voltage circuits provide power to the control module. The control module supports the following features:

After blow

The after blow feature is a retailer installed accessory. The after blow relay control circuit of the BCM and the after blow relay of the Instrument Panel Fuse Block are the items included in this option. The duration of the after blow sequence is determined by A/C operation, ambient air temperature and vehicle speed.

Mode Actuators - Defrost, Panel and Floor

The mode actuators are 5 wire bi-directional electric motors that incorporate a feedback potentiometer. Low reference, 5 volt reference, position signal, and 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 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, one of the control circuits is grounded. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module removes power from both control circuits.

The HVAC control module applies ground 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 module applies ground directly to the blower motor through the high blower motor control circuit. The resistor card has a fusible link which if blown, will require that the card be replaced.

The defrost, panel and floor actuators control air delivery. The HVAC control module controls these actuators in order to distribute airflow to a desired outlet. When the vehicle operator selects the defrost, mix-blend or floor positions, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. The flow of air during the various modes of operation is as follows:

The recirculation actuator is a 2-wire bi-directional electric motor. Two control circuits enable the actuator to operate. The control circuits use either ground or a 12-volt value to co-ordinate the actuator movement. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. The recirculation operation can function with blower motor in either the ON or OFF position. The A/C compressor automatically comes on when recirculation is selected. Recirculation is not available in defrost, mix-blend or floor mode. The recirculation LED may still be on while the air inlet door is in the outside air position.