Heating and A/C System

HEATING AND A/C SYSTEM

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. 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 valves 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.

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

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.

Compress 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.

Compress 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.