Automatic Temperature Control (ATC)

AUTOMATIC TEMPERATURE CONTROL (ATC)

SYSTEM CONTROLS
The ATC Module:
- is fully addressable with the DRBIII(R).
- The DRBIII(R) communicates with the ATC Module through the Diagnostic Link Connector (DLC) via a K-Line.
- communicates with other modules over the Controller Area Network (CAN) C Bus.
- controls A/C clutch operation.
- controls EBL operation.
- controls water cycle valve operation.
- The water cycle valve is a normally open valve, meaning that it allows full engine coolant flow through the heater core when no power is delivered to the valve. The ATC controls the valve with a pulse width signal. The lower the percentage of the pulse width signal the more the valve is open.
- controls Residual Heat Utilization (REST) function.
- controls blower motor operation, providing four blower speeds (Low, M1, M2, & High).
- controls recirculation air solenoid valve.
- controls the mode door via cables.
- controls the main power supply to the Heater Booster (if equipped).
- uses air inlet temperature sensor, air outlet temperature sensor, and evaporator temperature sensor input, as well as data from other modules to maintain occupant comfort levels.

SYSTEM DIAGNOSTICS
Fault detection is through active and stored Diagnostic Trouble Codes (DTCs)
- DTCs are displayed by the DRBIII(R).
- Active DTCs are those which currently exist in the system. The condition causing the fault must be repaired in order to clear this type of DTC.
- Stored DTCs are those which occurred in the system since the ATC Module received the last clear diagnostic info message.

Testing Preparation & Diagnostics
Set the necessary system functions accordingly so that all of the following prerequisites are met prior to performing diagnostic tests on the ATC system:
1. Connect the DRBIII(R) to the DLC.
2. Place the shift lever in park.
3. Start the engine.
4. Set the blower to high speed.
5. Set the temperature selector to full cold.
6. Press air conditioning switch on.
7. With the DRBIII(R) in Sensors, verify that the:
a. ambient temperature is above 59° F (15° C).
b. refrigerant pressure is between 29 and 348 PSI (2 and 24 bar).
c. evaporator temperature is above 36.5° F (2.5° C).
d. coolant temperature is above 158° F (70° C).

When all of the prerequisites have been met, use the DRBIII(R) to record and erase all stored ATC DTCs, and then select System Tests, and run the ATC Function Test. When complete, check to see if any active DTCs are present. If so, refer to the symptom list in the Heating & A/C category for the diagnostic procedure(s). If there are no DTCs present, yet the performance seems less than ideal, use the DRBIII(R) to look at all sensor values and the status of the various inputs and outputs to see if there is a deficiency detected that has not fully shut down the system. For additional information, refer to Sensor Values and Input/Output Status under Diagnostic Tips and for evaporator temperature sensor and air outlet temperature sensor resistance to temperature specifications charts. Also, confirm that the water cycle valve is functioning. Remember that the valve is normally open. The pulse width signal will offer insight into the valve's operation. The lower the percentage number, the more open the valve becomes. Confirm that the valve is responding to the signal from the ATC. If functioning correctly, verify mode and blend door operation. If okay, the diagnosis then becomes purely refrigerant system related. Attach the appropriate gauges and diagnose the refrigeration system. Refer to the Service Information for refrigerant system diagnostic procedures.

DIAGNOSTIC TIPS

SENSOR VALUES

Ambient Air Temperature
The Instrument Cluster transmits Ambient Air Temperature Sensor data. In the event of a CAN Bus communication failure, the last stored value is displayed as a substitute value.

Interior Temperature
The normal range for the Interior Temperature Sensor is from 32° F to 104° F. An implausible temperature value indicates that the Interior Temperature Sensor is bad. The repair in this case would be to replace the ATC Module since the sensor is integral to the module.

Evaporator Temperature
The normal range for the Evaporator Temperature Sensor is from 14° F to 104° F. A substitute value of 14° F with no updates indicates an Evaporator Temperature Sensor circuit failure.

Air Outlet Temperature
The normal range for the Air Outlet Temperature Sensor is from 32° F to 203° F. A substitute value of 111.1° F indicates an Air Outlet Temperature Sensor circuit failure.

Coolant Temperature
The Engine Control Module transmits Coolant Temperature Sensor date. In the event of a CAN Bus communication failure, 257° F is displayed as a substitute value.

Interior Temperature Controller
The normal range for the Blend control is from 62° F to 144° F. This value represents the temperature set by the operator. An implausible temperature value or a temperature value that fails to change when rotating the Blend control indicates that the Blend control is bad. The repair in this case would be to replace the ATC Module since the Blend control integral to the module.

Refrigerant Pressure
The normal range for the Refrigerant Pressure Sensor is from 29 PSI to 406 PSI. A substitute value of 413 PSI indicates a Refrigerant Pressure Sensor circuit failure. In addition, the normal range for Pressure Sensor voltage is 0 volts to 5 volts. A value of 0.9 volts indicates an open voltage supply circuit, while a value of -999 indicates an open in all three sensor circuits.

Water Cycle Valve
The normal range of the Water Cycle Valve is from 0% to 100%. The value indicates the extent to which the valve is closed. A value of 100% indicates that the valve is fully closed.

Intense Inst Light
The Instrument Cluster transmits this data. The normal range for lighting intensity is from 0% to 100%. The value indicates the extent to which the illumination has dimmed. A value of 0% indicates bright while a value >0% indicates dimming. In the event of a CAN Bus communication failure, 0% is displayed as a substitute value.

INPUT/OUTPUT STATUS

Compressor Clutch
The ATC Module transmits this data. A status of ON indicates that the compressor is operational. A status of OFF indicates the compressor is not operational.

Compres SO Accel (Compressor Shut Off - Due To Acceleration)
The Engine Control Module transmits this data. A status of YES indicates that the compressor shut off because of an acceleration request. A status of NO indicates that there is no acceleration request. If shut off due to an acceleration request, the compress will switch on again after 20 seconds. In addition, the original acceleration request can no longer exist for the ECM to acknowledge a subsequent request. In the event of a CAN Bus communication failure, NO is displayed as a substitute value.

Compres SO W/E-Off (Compressor Shut Off -Due to Emergency Off)
The Engine Control Module transmits this data. A status of YES indicates that the compressor shut off because of an emergency off request. A status of NO indicates that there is no emergency off request. In the event of a CAN Bus communication failure, the last stored value is displayed as a substitute value.

Auxiliary Fan
The ATC Module transmits this data. A status of ON indicates that the auxiliary fan is operational. A status of OFF indicates that the auxiliary fan is not operational. The Auxiliary Fan normally operates when refrigerant head pressure exceeds 290 PSI and coolant temperature exceeds 221° F. In the event of a CAN Bus communication failure, 257° F is displayed for coolant temperature (in Sensors) and the Auxiliary Fan will run continuously.

Light PB CTRL Module
This input displays a status of "Bright" for positive dimmer switch operation and "Dimmed" for negative dimmer switch operation. In the event of a CAN Bus communication failure, "Bright" is displayed.

CABIN HEATER MODULE (CHM) & HEATER BOOSTER MODULE (HBM)

SYSTEM DESCRIPTION

WARNING:
- NEVER OPERATE THE HEATER IN AN ENCLOSED AREA THAT DOES NOT HAVE EXHAUST VENTILATION FACILITIES. ALWAYS VENT THE HEATER'S EXHAUST WHEN OPERATING THE HEATER. REFER TO "VENTING THE HEATER'S EXHAUST" BELOW FOR PROPER EXHAUST VENTING INSTRUCTIONS. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.
- ALLOW THE HEATER ASSEMBLY TO COOL BEFORE PERFORMING A COMPONENT INSPECTION/REPAIR/REPLACEMENT. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.
- ALWAYS DISCONNECT THE VEHICLE'S BATTERY PRIOR TO PERFORMING ANY TYPE OF WORK ON THE HEATER ASSEMBLY. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.
- NEVER ATTEMPT TO REPAIR THE HEATER ASSEMBLY OR ANY OF ITS INTERNAL COMPONENTS. ALWAYS PERFORM HEATER COMPONENT REPLACEMENT IN ACCORDANCE WITH THE SERVICE INFORMATION. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.

CAUTION: Always Perform The Heater Pre-Test (In The Diagnostic Procedures) Prior To Performing Any Other Test On The Heater For The Test Result To Be Valid.

NOTE:
- Do not disconnect the vehicle's battery or the heater's main power-supply while the heater is in operation or in run-down mode. Failure to follow these instructions may result in excess emissions from the heater.
- Failure to prime the Dosing Pump after draining the fuel line will prevent heater activation during the first attempt to start the unit. This may also set a Diagnostic Trouble Code (DTC) in the control unit's memory. Do not perform the Dosing Pump Priming Procedure if an attempt was made to start the heater without priming the Dosing Pump first. This will put excess fuel in the heater module and cause smoke to emit from the heater's exhaust pipe when heater activation occurs.
- Waxed fuel can obstruct the fuel line and reduce flow. Check for the appropriate winter grade fuel and replace as necessary.

The Cabin Heater Assembly and Heater Booster Assembly are supplemental type heaters designed to pre-heat the engine's coolant in order to supply the vehicle's occupants with heat prior to the engine reaching operating temperature. The heater's control unit controls and monitors combustion operation through various inputs and outputs that are contained inside the heater assembly. The supplemental heater connects to the vehicle's heater hoses and uses a separate fuel supply line and fuel pump that connects to the vehicle's fuel tank. Unlike the Heater Booster, the Cabin Heater Assembly has an integral coolant pump which allows heater operation without the vehicle's engine running. In addition, a programmable timer module can also be added to this system. Neither the Cabin Heater Assembly nor the Heater Booster Assembly are connected to the CAN Bus. Communication between the heater's control unit and the DRBIII(R) occurs through the Diagnostic Link Connector (DLC) via a K-Line.

VENTING THE HEATER'S EXHAUST

WARNING:
- NEVER OPERATE THE HEATER IN AN ENCLOSED AREA THAT DOES NOT HAVE EXHAUST VENTILATION FACILITIES. ALWAYS VENT THE HEATER'S EXHAUST WHEN OPERATING THE HEATER. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.
- ALLOW THE HEATER ASSEMBLY TO COOL BEFORE PERFORMING A COMPONENT INSPECTION/REPAIR/REPLACEMENT. FAILURE TO FOLLOW THESE INSTRUCTIONS CAN RESULT IN PERSONAL INJURY OR DEATH.

CAUTION: When using a powered exhaust ventilation system, do not attach the exhaust ventilation hose directly to the heater's exhaust pipe. Too much suction can prevent heater operation.

When using a powered exhaust ventilation system, affix the ventilation hose to the heater's exhaust pipe or to the vehicle in such a manor that the end of the ventilation hose remains approximately three inches away from the end of the heater's exhaust pipe.

When using a non-powered exhaust ventilation system, affix the ventilation hose directly to the heater's exhaust pipe.

SYSTEM DIAGNOSTICS

CAUTION: Always Perform The Heater Pre-Test (In The Diagnostic Procedures) Prior To Performing Any Other Test For The Test Result To Be Valid.

Fault detection is through stored Diagnostic Trouble Codes (DTCs). DTCs are displayed by the DRBIII(R). The heater's control unit will store up to five DTCs in its memory. If the control unit detects a new fault in the system, one that is not already stored in its memory, it will clear the oldest of the five stored DTCs, and it will store the new fault's DTC. If the control unit detects a reoccurrence of a stored fault, it will overwrite that fault's DTC with the most recent occurrence.

DIAGNOSTIC TIPS

SENSOR VALUES

Operating Voltage
The normal range for the Operating Voltage is from 10 volts to 15 volts. The value indicates the voltage at the heater's Fused B+ terminal.

Heating Capacity
The normal range for the heating capacity is from 0% to 100%. The value indicates the momentary output of the auxiliary heater in % of the maximum output.

Coolant Temperature
The value indicates the current coolant temperature.

Flame Sensor Resistance
The normal range for the Flame Sensor is from 750 ohms to 2270 ohms. The value indicates the momentary resistance of the Flame Sensor.

INPUT/OUTPUT STATUS

Dosing Pump
A status of ON indicates that the Dosing Pump is operational. A status of OFF indicates the Dosing Pump is not operational.

Glow Pin
A status of ON indicates that the Glow Pin is energized. A status of OFF indicates the Glow Pin is not energized.

Combustion Fan
A status of ON indicates that the Combustion Fan is operational. A status of OFF indicates the Combustion Fan is not operational.

Circulation Pump
A status of ON indicates that the Circulation Pump is operational. A status of OFF indicates the Circulation Pump is not operational.

Front End Blower
A status of ON indicates that the Blower Motor is operational. A status of OFF indicates the Blower Motor is not operational.

Static Heater Signal
A status of ON indicates that the heater module sees the Stationary Heating Mode ON signal after switching on the heater with the heater timer or the auxiliary heater switch. A status of OFF indicates that the Stationary Heating Mode ON signal is not present at the heater module.

Heater Booster Mode Signal
A status of ON indicates that the heater module sees the Heater Booster Mode ON signal after switching on the heater with the auxiliary heater switch. A status of OFF indicates that the Heater Booster Mode ON signal is not present at the heater module.