Part 2 of 2
HEATING & A/C SYSTEMThe all-new heating and air conditioning system for DN provides more heating and cooling capacity than in previous years. Depending on the model, either a Dual-Zone Air Conditioning System or a Three-Zone Air Conditioning System is currently available in these vehicles.
Air Distribution (Front)
The front compartment HVAC unit has four fully adjustable instrument panel outlets. Side-window demister outlets in the instrument panel eliminate the need for door ducts and door-to-instrument panel seals. A single central mounted outlet delivers air for defrosting the windshield. Two outlets, one on each side of the center console underneath the instrument panel, provide airflow to the driver floor area and to the front seat passenger floor area. While two additional outlets, one on each side of the center console near the rear of the front seats, distribute both heated and cooled air across the floor to the intermediate seat passengers. Ducts in the center of the vehicle underneath the carpet deliver air from the front compartment HVAC unit to the two intermediate passenger outlets.
Door Actuator Control
A simplified control system for operation of the mode, recirculation, and temperature control actuators provides positive positioning without the complexity of feedback from position sensors. The A/C - Heater Control Module knows the number of operating actuator revolutions required for full door travel as well as the number of actuator commutator pulses per revolution. Using these parameters, the A/C - Heater Control Module runs the actuator for the number of commutator pulses that correspond to the desired door position. To maintain accuracy, the system recalibrates itself periodically at known zero and full travel conditions.
The dual sliding Blend switches have multiple detents to control the full range of temperature that the system can produce in any mode. On Dual-Zone systems, the upper slide pot controls the driver-side blend door and the lower slide pot controls the passenger-side blend door. On Three-Zone systems, the upper slide pot controls the driver-side blend door, while the lower slide pot controls the passenger-side blend door and the rear A/C - heater unit blend door.
The single rotary Mode switch has 12 detents to either direct airflow to the panel outlets, to a mix of floor and panel outlets, to the floor outlets, to a mix of floor and defrost outlets, or to the defrost outlet. Rotating the Mode switch to either of the two MAX positions results in the A/C - Heater Control Module sending a signal to the recirculation actuator to close the fresh-air door. While rotating the Mode switch to any other position results in the A/C - Heater Control Module sending a signal to the recirculation actuator to open the fresh-air door.
When the Blower switch is OFF, the A/C - Heater Control Module closes the fresh-air door to prevent outside air from entering the vehicle. On Three- Zone systems, the Mode switch also controls the rear A/C - heater unit mode door, which directs rear airflow either to the right quarter trim panel outlet or to the overhead outlets.
Front Blower Control
The front blower circuitry employs a new resistor technology to control front blower speed. Called the "credit card" resistor, the device looks much like its name in that it is thin and compact like a credit card. The credit card resistor, like the coil resistor used in previous years, mounts inside the front HVAC housing assembly in the airflow path. However, unlike the coil resistor, the credit card resistor offers much less airflow restriction.
A/C Operation
The A/C - Heater Control Module monitors the temperature of the evaporator to keep it just above freezing for maximum cooling and dehumidification. A thermistor (temperature variable resistor) placed between the evaporator fins provides the signal for the control. The Powertrain Control Module (PCM) cycles the compressor on and off with a signal from the A/C - Heater Control Module.
Heater Operation
To assist the HVAC system in maintaining a consistent and optimum heat output at low vehicle speeds, an electric coolant pump operates under specific conditions to keep a steady flow of hot coolant circulating through the heater circuit. The A/C - Heater Control Modules controls the operation of the electric coolant pump. The pump runs when all of the following conditions are met: When the vehicle's speed is below 27 Km/h (17 mph), the coolant temperature is between 65.5 °C and 110 °C (150 °F and 230 °F), and the blend control is set above 60% reheat. The A/C - Heater Control Module turns the pump OFF if any one of the following conditions occur: The vehicle speed rises above 48.3 Km/h (30 mph). The coolant temperature drops below 65.5 °C (150 °F). The coolant temperature rises above 110 °C (230 °F). The blend control is set below 60% reheat.
A/C - Heater Control (Rear)
The Three-Zone system allows the intermediate seat occupants to regulate the air temperature and the fan speed of the rear unit from the rotary controls on the headliner mounted Rear A/C - Heater Control.
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 Cool down Test to test A/C system performance and the HVAC Door Recalibration Test to determine actuator travel span. After 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. Stored DTCs are faults that occurred in the HVAC system since the control module received the last "clear diagnostic info" message.
INTERIOR LIGHTING
The Courtesy lights and illuminated entry feature are controlled by the Central Timer Module (CTM). The CTM will activate the courtesy lamps, including Map Lights and the Dome Lights when either the dome lamp switch is turned ON or a door is opened. The courtesy lamps will fade to OFF immediately when all doors are closed with the dome lamp switch in the OFF position.
The illuminated entry feature operates under the following conditions:
- RKE "unlock"
- Driver/Passenger door is opened
- Unlocking either the driver or passenger using the key (vehicles equipped with security system)
- The dome lamp switch is turned ON
Once activated, the illuminated entry will "fade to OFF" after 3 to 5 seconds under the following conditions:
All doors are closed and:
- RKE "lock signal is received or
- Manual actuated power "lock" signal is received or
- Ignition switch is turned to the ON position or
- 30 seconds have elapsed without any other action
Addition RKE unlock actuation before the expiration of illuminated entry will not reset timer. Opening any door before the 30 second timer expires, will reset the entry time to 30 seconds and the illuminated entry timer will not begin counting down again until all doors are closed.
The Cargo lamps are controlled by the CTM. Placing the dome lamp switch in the cargo lamp position grounds an input to the CTM. The CTM then sends voltage to the cargo lamps.
The Interior lamp defeat feature will not allow any interior lamp to be turned ON. This is accomplished through an input to the CTM from the dome lamp switch.
The CTM provides battery protection by shutting down the interior lamps due to the following.
Leaving a door open, dome lamp switch ON, reading/vanity lamp switch ON or glove box door open for more than 15 minutes while the ignition is OFF.
POWER DOOR LOCKS/REMOTE KEYLESS ENTRY
The CTM controls the door lock actuator assemblies to handle locking and unlocking with the key fob or interior switch.
Vehicles that are equipped with the Vehicle Theft Security System will also have the central locking feature. With the central locking feature, when the cylinder lock switch is turned to the lock position all the doors will lock. For unlocking, if the key is turned to the unlock position once, only that door will unlock. If the key is then turned a second time to the unlock position, all the doors will unlock.
There is also a door lock inhibit feature that prevents power locking of the doors if the ignition is OFF and the key is in the ignition.
Automatic or "rolling locks" are included as a programmable feature. If the vehicle is moving approximately 15 mph and approximately 10 degrees of throttle opening is seen by the PCM, (the PCM will send this info to the CTM via the PCI bus) indicating acceleration, the CTM will cycle the lock actuators to lock the doors.
The highline CTM provides for Remote Keyless Entry (RKE)
The RKE system is placed in the programming mode by the DRB III, or by the customer program features. The system will store up to four key fob codes. Two fobs are supplied with the truck, additional fobs may be purchased through the parts department. Through the DRB III, erasing and programming of one key fob without deleting the others is possible. If the key fob is stolen, all the fob codes stored previously may be erased to provide the owner of the vehicle with an extra sense of security.
VEHICLE COMMUNICATION
The Programmable Communication Interface or PCI Bus is a single wire multiplexed network capable of supporting binary encoded messages shared between multiple modules. The PCI bus circuit is identified as D25 and is violet with a yellow tracer. Additional tracer colors may be added to the yellow in order to distinguish between different module connections. The modules are wired in parallel. Connections are made in the harness using a splice.
The splice called the Diagnostic Junction Port, serves as the "Hub" of the bus. The Diagnostic Junction Port provides an access point to isolate most of the modules on the bus in order to assist in diagnosing the circuit. The following modules are used on the DN:
- Airbag Control Module
- A/C Heater Control
- Central Timer Module
- Controller Antilock Brake
- Compass Mini-Trip Computer
- Electro/Mechanical Instrument Cluster
- Powertrain Control Module
- Radio
- Sentry Key Immobilizer Module
- Transfer Case Control Module
- Transmission Control Module
Each module provides its own bias and termination in order to transmit and receive messages. The bus voltage is at zero volts when no modules are transmitting and is pulled up to about seven and a half volts when modules are transmitting.
The bus messages are transmitted at a rate averaging 10800 bits per second. Since there is only voltage present when the modules transmit and the message length is only about 500 milliseconds, it is ineffective to try and measure the bus activity with a conventional voltmeter. The preferred method is to use the DRB III lab scope. The 12v square wave selection on the 20-volt scale provides a good view of the bus activity. Voltage on the bus should pulse between zero and about seven and a half volts. Refer to the figure for some typical displays.
The PCI Bus failure modes are broken down into two categories. Complete PCI Bus Communication Failure and individual module no response. Causes of complete PCI Bus Communication Failure include a short to ground or battery on the PCI circuit. Individual module no response can be caused by an open circuit at either the Diagnostic Junction Port or the module, or an open battery or ground circuit to the affected module.
Symptoms of a complete PCI Bus Communication
Failure would include but are not limited to:
- All gauges on the EMIC stay at zero
- All telltales on EMIC illuminate
- EMIC backlighting at full intensity
- Dashed lines in the Compass Mini-Trip Computer display
- No response received from any module on the PCI bus (except the PCM)
- No start (if equipped with Sentry Key immobilizer)
Symptoms of Individual module failure could include any one or more of the above. The difference would be that at least one or more modules would respond to the DRB III.
Diagnosis starts with symptom identification. If a complete PCI Bus Communication Failure is suspected, begin by identifying which modules the vehicle is equipped with and then attempt to get a response from the modules with the DRB III. If any modules are responding, the failure is not related to the total bus, but can be caused by one or more modules PCI circuit or power supply and ground circuits. The DRB III may display "BUS +A SIGNAL OPEN" or "NO RESPONSE" to indicate a communication problem. These same messages will be displayed if the vehicle is not equipped with that particular module. The CCD error message is a default message used by the DRB III and in no way indicates whether or not the PCI bus is operational. The message is only an indication that a module is either not responding or the vehicle is not equipped.
VEHICLE THEFT SECURITY SYSTEM
The VTSS system monitors the door ajar switches, and ignition switch to detect unauthorized entry into the vehicle. Once the vehicle is "armed", any one of these inputs can cause the VTSS system to be tripped. Once tripped, the horn and lights will pulse for 3 minutes and if an attempt is made to start the engine with a non-programmed SKIM key, it will start and stall. If the trigger condition is still present, the lights will continue to flash for an additional 15 minutes, after which the system will stop pulsing the lights and return to the "armed" state. The cause of the last 4 alarm triggers is stored by the CTM and may be retrieved by the DRB III. The system may be disarmed by either an unlock command from a valid RKE key fob by using a key in either door, or by using a valid SKIM key in the ignition. The door key cylinders are equipped with disarm switches. There is also a VTSS lamp on the dash that provides information to the driver about the state of the vehicle theft system.
WINDSHIELD WIPER SYSTEM
The DN truck is equipped with speed sensitive intermittent wipers. The low and high speeds are controlled through the wiper stalk switch. The intermittent portion of the wiper control is handled by the CTM through the intermittent wiper relay. When the module detects a decrease in delay time as selected by the driver, an immediate wipe of the windshield takes place and the new delay interval is implemented.