Manual Temperature Control (MTC)

SYSTEM AVAILABILITY
Depending on the model, either a Single-Zone Air Conditioning System or a Dual-Zone Air Conditioning System is currently available in these vehicles. For domestic vehicles, a Three Zone Air Conditioning System is also available.

Cabin Heater
For export vehicles equipped with a diesel engine, a Cabin Heater is used in conjunction with the HVAC system. The Cabin Heater is designed to supply the vehicle's occupants with heat prior to the engine reaching operating temperature. For additional information on this system, refer to Cabin Heater under General Information and Diagnostic Procedures.

Zone Control
The Single-Zone Air Conditioning System maintains incoming air temperature, airflow, fan speed, and fresh air intake for the entire vehicle from the instrument panel mounted A/C-Heater Control Module. The full range of temperature that the system can produce in any mode for the entire vehicle is available by positioning the blend control to the desired range.

The Dual- and Three-Zone Air Conditioning systems allow completely independent side-to-side control of incoming air temperature. The full range of temperature that the front system can produce in any mode is available on either side of the vehicle by positioning the independent driver and passenger blend controls to the desired range. The three- zone system also allows the front seat occupants to completely control the Rear A/C-Heater Unit from the instrument panel mounted A/C-Heater Control Module. The intermediate and rear seat occupants can also regulate the air temperature and the fan speed of the rear unit from the rotary controls on the headliner mounted Rear Blower Rear Control.

Front HVAC Unit
The front compartment HVAC has five fully adjustable instrument panel outlets. Side-window demister outlets in the instrument panel eliminate door ducts and door-to-instrument panel seals. A single, central mounted outlet delivers air for defrosting the windshield. Air exhausters allow air entering at the front of the vehicle to flow out of the back to the rear occupants. Wide outlets under the front seats with directional dividers distributes the heated or cooled air across the floor to the intermediate seat occupants. Ducts in the center of the vehicle under the carpet deliver air from the front compartment HVAC unit to these outlets. Overhead outlets along the roof rails adjacent to each rear seat and three outlets in the right quarter panel near the floor distribute air to the intermediate and rear seat occupants. Models equipped with Dual- Zone and Three-Zone A/C systems include a dust and odor air filter.

Rear HVAC Unit
The rear A/C-Heating unit provides air temperature modulation by utilizing a temperature door to allow variable proportions of cooled and heated air to mix to achieve a desired ambient temperature. Also a variable mode control in the rear unit allows proportioned airflow between the floor and overhead outlets.

A/C-Heater Control Module, Switch Operation

Power Switch
The Power Switch is a momentary contact switch. The switch status indicator illuminates when the switch is on. The Power Switch setting is remembered during power down.

Rear Window Defogger Switch
The Rear Window Defogger Switch is a momentary contact switch. Toggling the switch results in the A/C-Heater Control Module sending a change of state message to the FCM to provide rear window defogger activation or deactivation respectively. The switch status indicator illuminates when the switch is on.

Recirculation Switch
The Recirculation Switch is a momentary contact switch. Toggling the switch on results in the A/C-Heater Control Module signaling the actuator to close the fresh-air door. Toggling the switch OFF results in the A/C Heater Control Module signaling the actuator to open the fresh-air door. The switch status indicator illuminates when the switch is on. When the Power Switch is OFF, the A/C-Heater Control Module closes the fresh-air door to prevent outside air from entering the passenger compartment. The recirculation mode will cancel whenever defrost is requested. Pressing the Recirculation Switch while in defrost mode will illuminate the Recirculation Switch status indicator, but only while the button is pressed. Under this circumstance, the recirculation request will be denied and the fresh-air door will remain in the fresh position. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C-Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

A/C Switch
The A/C Switch is a momentary contact switch. Toggling the switch results in the A/C-Heater Control Module sending a change of state message to the PCM to provide A/C compressor clutch activation or deactivation respectively. The A/C-Heater Control Module will only provide this request if EVAP function is found acceptable. The Power Switch must be on to make the A/C switch active. The switch status indicator illuminates when the switch is on. The A/C Switch setting is remembered during power down.

Blower Switch - Front
The rotary Blower Switch has five positions, Low, M1, M2, M3, and High. The Power Switch must be on to make the Blower Switch active. Toggling the Power Switch results in the A/C-Heater Control Module sending a request to the FCM to provide blower motor activation or deactivation respectively.

Blower Switch - Rear Blower Front Control Switch
The rotary Blower Switch has five positions, Rear, Off, Low, Med, and High. The Power Switch must be on to make the Blower switch active. The Blower Switch must be in the Rear Position to make the Rear Blower Rear Control active. Toggling the Power Switch results in the A/C-Heater Control Module sending a request to the FCM to provide blower motor activation or deactivation respectively.

Blend Switch - Single Zone
The single rotary Blend Switch has multiple detents to control the full range of temperature that the system can produce in any mode. Rotating the switch results in the A/C-Heater Control Module signaling the actuator to move the blend door. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C-Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

Blend Switch - Dual and Three-Zone
The dual sliding Blend Switches have multiple detents to control the full range of temperature that the system can produce an any mode. On Dual-Zone systems, the upper slide pot controls the driver-side blend door, while the lower slide pot controls the passenger-side blend door. On Three-Zone systems, the upper slide pot controls the driver-side blend door and, when activated, the Rear A/C-Heater Unit Blend Door. The lower slide pot controls the passenger-side blend door. Sliding the switch results in the A/C-Heater Control Module signaling the actuator to move the blend door. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C-Heater Control Module runs the actuator for the number of pulses Corresponding to the desired door position.

Mode Switch - Single- and Dual-Zone
The single rotary Mode Switch has 13 detents to either direct airflow to the panel outlets, a mix of floor and panel outlets, floor outlets, a mix of floor and defrost outlets, or defrost outlets. Rotating the switch results in the A/C-Heater Control Module signaling the actuator to move the mode door. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C-Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

Mode - Three-zone
The single, rotary Mode Switch has 13 detents to either direct airflow to the panel outlets, a mix of floor and panel outlets, floor outlets, a mix of floor and defrost outlets, or defrost outlets. When the Rear A/C-Heater Unit is activated, the Mode Switch also controls its Mode Door to direct the rear airflow to the floor or overheard outlets. Rotating the switch results in the A/C-Heater Control Module signaling the actuator to move the mode door(s). All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C-Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

Rear Blower Rear Control

Switch Operation
The A/C- Heater Control Module's Power Switch must be on to make the Rear Blower Front Control Switch active. The Rear Blower Front Control Switch must be in the Rear position to make the Rear Blower Rear Control active.

Blower Switch
The rotary Blower Switch has three positions, Low, Med, and High. Toggling the A/C-Heater Control Module's Power Switch on and positioning the Rear Blower Front Control Switch in the Rear position results in the A/C-Heater Control Module sending a request to the FCM to provide blower motor activation. Toggling the A/C-Heater Control Module's Power Switch OFF or rotating the Rear Blower Front Control Switch OFF of the Rear position results in the A/C-Heater Control Module sending a request to the FCM to provide blower motor deactivation.

Blend Switch
The rotary Blend Switch controls the full range of temperature that the rear system can produce in any mode. Rotating the switch results in the A/C-Heater Control Module signaling the actuator to move the blend door. A low temperature setting directs airflow to the overhead outlets, while a high temperature setting directs airflow to the floor outlets. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C-Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

HVAC Diagnostics
The A/C-Heater Control Module is fully addressable with the DRB III. Two of the Control Module's diagnostic capabilities that the DRB III will actuate include the A/C Cooldown Test to test A/C system performance and the HVAC Door Recalibration Test to determine actuator travel span. Alter performing either test, the Control Module will display one or more messages on the DRB III screen. The message will indicate either that the HVAC system passed the test or that there is a fault currently active in the HVAC system. The DRB III can also extract active and stored Diagnostic Trouble Codes (DTCs) from the control module. Active DTCs are faults that currently exit in the HVAC system. Active DTCs will not clear until the condition causing the code is repaired. Stored DTCs are faults that occurred in the HVAC system since the control module received the last "clear diagnostic info" message.