Climate Control System
Climate Control System
WARNING: Take the following precautions when repairing an air conditioning system containing R-134a:
- Always wear safety goggles.
- Avoid contact with liquid refrigerant R-134a. R-134a vaporizes at approximately -25°C (-13°F) under atmospheric pressure and will freeze skin tissue.
- Never allow refrigerant R-134a gas to escape in quantity in an occupied space. It will displace the oxygen needed to support life.
- Never use a torch in an atmosphere containing R-134a gas. R-134a is non-toxic at all normal conditions, but it decomposes when exposed to high temperatures such as a torch flame. During decomposition it releases irritating and toxic gasses (as described in the MSDS sheet from the manufacturer). Decomposition products are hydrofluoric acid, carbon dioxide and water.
Failure to follow these instructions may result in serious personal injury.
NOTICE: To avoid damaging the vehicle or Air Conditioning (A/C) components, the following precautions must be observed.
- The A/C refrigerant of all vehicles must be identified and analyzed prior to refrigerant charging. Failure to do so can contaminate the shop bulk refrigerant and other vehicles.
- Do not add R-12 refrigerant to an A/C system that requires the use of R-134a refrigerant. These 2 types of refrigerant must never be mixed. Doing so can damage the A/C system.
- Charge the A/C system with R-134a refrigerant gas while the engine is running only at the low-pressure side to prevent refrigerant slugging from damaging the A/C compressor.
- Use only R-134a refrigerant. Due to environmental concerns, when the A/C system is drained, the refrigerant must be collected using refrigerant recovery/recycling equipment. Federal, State/Provincial and/or local laws REQUIRE that R-134a be recovered into appropriate recovery equipment and the process be conducted by qualified technicians who have been certified by an approved organization, such as ASE, Mobile Air Conditioning Society (MACS). Use of a recovery machine dedicated to R-134a is necessary to reduce the possibility of oil and refrigerant incompatibility concerns. Refer to the instructions provided by the equipment manufacturer when removing refrigerant from or charging the A/C system.
- Refrigerant R-134a must not be mixed with air for leak testing or used with air for any other purpose above atmospheric pressure. R-134a is combustible when mixed with high concentrations of air and higher pressures.
- A number of manufacturers are producing refrigerant products that are described as direct substitutes for refrigerant R-134a. The use of any unauthorized substitute refrigerant can severely damage the A/C components. If repair is required, use only new or recycled refrigerant R-134a.
NOTICE: To avoid contamination of the Air Conditioning (A/C) system, the following precautions must be observed.
- Never open or loosen a connection before recovering the refrigerant.
- When loosening a connection, if any residual pressure is evident, allow it to leak out before opening the fitting.
- Evacuate a system that has been opened to install a new component or one that has discharged through leakage before charging.
- Seal open fittings with a cap or plug immediately after disconnecting a component from the system.
- Clean the outside of the fittings thoroughly before disconnecting a component from the system.
- Do not remove the sealing caps from a new component until ready to install.
- Refrigerant oil will absorb moisture from the atmosphere if left uncapped. Do not open an oil container until ready to use and install the cap immediately after using. Store the oil in a clean, moisture-free container.
- Install a new O-ring seal before connecting an open fitting. Coat the fitting and O-ring seal with mineral oil before connecting.
- When installing a refrigerant line, avoid sharp bends. Position the line away from the exhaust or any sharp edges that can chafe the line.
- Tighten threaded fittings only to specifications. The steel and aluminum fittings used in the refrigerant system will not tolerate overtightening.
- When disconnecting a fitting, use a wrench on both halves of the fitting to prevent twisting of the refrigerant lines or tubes.
- Do not open a refrigerant system or uncap a new component unless it is as close as possible to room temperature. This will prevent condensation from forming inside a component that is cooler than the surrounding air.
The climate control system consists of the following components:
- A/C compressor
- A/C compressor clutch assembly
- A/C condenser core with integral receiver/drier
- A/C evaporator core
- Connecting refrigerant lines
- Thermostatic Expansion Valve (TXV)
- A/C pressure transducer
- Heater core and evaporator core housing
- HVAC module - Electronic Manual Temperature Control (EMTC) or HVAC module - Dual Automatic Temperature Control (DATC)
- Temperature blend door actuators
- Defrost/panel/floor door actuator
- Air inlet door actuator
- Blower motor speed control
- Blower motor
- In-vehicle temperature sensor
- Sunload sensor
- Evaporator temperature sensor
Electronic Manual Temperature Control (EMTC) System
System Operation
The Electronic Manual Temperature Control (EMTC) system heats or cools the vehicle depending on the HVAC control panel selection.
- The control panel selection determines heating or cooling, air distribution and enables blower motor operation.
- The temperature control setting determines the air temperature.
- The blower motor switch varies the blower motor speed.
- During A/C operation, the system reduces the relative humidity of the air.
Remote Start System Behavior
When the remote start feature is used, the climate control system automatically sets certain parameters in an attempt to achieve a comfortable cabin temperature. These parameters are set based on outside air temperature. During remote start, the outside air temperature is continually evaluated and HVAC system behavior can change if the outside air changes between cold, moderate and warm temperatures.
For cold ambient air temperatures (below 0°C (32°F)):
- the airflow mode is set to FLOOR/DEFROST.
- the temperature is set to full HOT.
- the blower speed is set to HIGH.
- the air inlet mode is set to fresh air.
- the auxiliary electric heater is enabled if needed (diesel engines only).
For moderate ambient air temperatures (between 0°C (32°F) and 27°C (80°F)):
- the airflow mode is set to the last user setting.
- the temperature is set to the last user setting.
- the blower speed is set to the last user setting.
- the air inlet mode is set to the last user setting.
- the auxiliary electric heater is enabled if needed (diesel engines only).
For warm ambient air temperatures (above 27°C (80°F)):
- the airflow mode is set to MAX A/C.
- the temperature is set to full COOL.
- the blower speed is set to HIGH.
- the air inlet mode is set to RECIRC.
- the auxiliary electric heater is not enabled (diesel engines only).
System Airflow and Mode Description
Max A/C
When MAX A/C is selected:
- the air inlet door closes off outside air and admits only recirculated air.
- the RECIRC button is disabled and the indicator is illuminated. (RECIRC forced ON)
- the defrost/panel/floor door directs airflow to the instrument panel A/C registers.
- blended air temperature is available.
- the A/C request button is illuminated and disabled.
- the A/C compressor operates if the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
PANEL
When PANEL is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator ON), the air inlet door closes off outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator OFF), the air inlet door admits only outside air into the passenger compartment.
- the defrost/panel/floor door directs airflow to the instrument panel A/C registers.
- blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator ON), can the airflow temperature be cooled below the outside air temperature.
- the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
PANEL/FLOOR
When PANEL/FLOOR is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator ON), the air inlet door closes off outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator OFF), the air inlet door admits only outside air into the passenger compartment.
- the defrost/panel/floor door directs airflow to the floor duct and the instrument panel A/C registers. A small amount of airflow from the side window demisters and defrost duct is present.
- blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator ON), can the airflow temperature be cooled below the outside air temperature.
- the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
OFF
When OFF is selected:
- the RECIRC request button is disabled.
- the air inlet door closes off outside air and admits only recirculated air.
- the A/C request button is disabled.
- the blower motor is OFF.
FLOOR
When FLOOR is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator ON), the air inlet door closes off outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator OFF), the air inlet door admits only outside air into the passenger compartment.
- the defrost/panel/floor door directs airflow to the floor duct. A small amount of airflow from the defroster duct and side window demisters is present.
- blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator ON), can the airflow temperature be cooled below the outside air temperature.
- the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
FLOOR/DEFROST
When the FLOOR/DEFROST is selected:
- the RECIRC request button is disabled. The air inlet door opens, admitting only outside air into the passenger compartment.
- the defrost/panel/floor door actuator directs airflow to the floor duct, the defroster duct and the side window demisters.
- blended air temperature is available.
- the A/C request button indicates the last status and the indicator can be toggled. To reduce fogging, the A/C compressor operates automatically, regardless of indicator status, if the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
DEFROST
When DEFROST is selected:
- the RECIRC request button is disabled. The air inlet door opens, admitting only outside air into the passenger compartment.
- the defrost/panel/floor door directs airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
- blended air temperature is available.
- the A/C request button will indicate the last status and the indicator can be toggled. To reduce fogging, the A/C compressor will operate automatically, regardless of indicator status, if the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
Dual Automatic Temperature Control (DATC) System
System Operation
The Dual Automatic Temperature Control (DATC) system maintains the selected vehicle interior temperature by heating and/or cooling the air.
- During A/C operation, the system reduces the relative humidity of the air.
- The driver may override the automatic mode of operation.
- The temperature control setting determines the desired air temperature.
- The blower motor control override button varies the blower motor speed.
- The driver side and passenger side temperature settings can be individually controlled.
When the DATC system is set to AUTO the air distribution direction, blower motor speed and A/C compressor operation are automatically controlled based on the temperature(s) selected.
The DATC system manual override settings:
- allow the air distribution direction to be manually selected.
- allow the blower motor speed to be manually selected.
- allow recirculation mode to be manually selected in all modes except DEFROST. The A/C request can be cancelled by pressing the A/C request switch, turning the indicator OFF.
- allow A/C compressor operation to be manually selected except in DEFROST.
Remote Start System Behavior
When the remote start feature is used, the climate control system automatically sets certain parameters in an attempt to achieve a comfortable cabin temperature. These parameters are set based on outside air temperature. During remote start, the outside air temperature is continually evaluated and HVAC system behavior can change if the outside air changes between cold, moderate and warm temperatures.
For cold ambient air temperatures as determined by the HVAC module AUTO mode to request heat:
- the airflow mode is set to FLOOR/DEFROST.
- the temperature is set to 22°C (72°F).
- the blower speed is set to AUTO.
- the air inlet mode is set to AUTO.
- the auxiliary electric heater is enabled if needed (diesel engines only).
For moderate ambient air temperatures as determined by the HVAC module AUTO mode to request heat or cooling:
- the airflow mode is set to the AUTO.
- the temperature is set to the last user setting (Temperature setting is limited to 18°C (65°F) minimum and 29°C (85°F) maximum. If the temperature is set above or below that range, it will use the minimum or maximum value.).
- the blower speed is set to the AUTO.
- the air inlet mode is set to AUTO.
- the auxiliary electric heater is enabled if needed (diesel engines only).
For warm ambient air temperatures as determined by the HVAC module AUTO mode to request cooling:
- the airflow mode is set to AUTO.
- the temperature is set to 22°C (72°F).
- the blower speed is set to AUTO.
- the air inlet mode is set to AUTO.
- the auxiliary electric heater is not enabled (diesel engines only).
System Airflow and Mode Description
AUTO
When AUTO is selected:
- the temperature control setting is manually set to the desired setting.
- the air inlet door is automatically controlled by the HVAC module, based on the temperature setting.
- the mode door is automatically controlled by the HVAC module, based on the temperature setting.
- the temperature blend doors are automatically controlled by the HVAC module, based on the temperature setting.
- the A/C compressor is automatically controlled by the HVAC module, based on the temperature setting. The A/C compressor will not operate if the outside temperature is below approximately 0°C (32°F).
- the A/C request button or the RECIRC request button, if pressed, transfers the system to semi-auto operation.
- the blower motor is ON. The blower motor speed is automatically controlled by the HVAC module, based on the temperature setting, but can be manually overridden.
OFF
When OFF is selected:
- the RECIRC request button is disabled.
- the air inlet door closes off outside air and admits only recirculated air.
- the defrost/panel/floor door actuator is in the DEFROST position.
- the A/C request button is disabled.
- the blower motor is OFF.
Max A/C
When MAX A/C is selected:
- the air inlet door closes off outside air and admits only recirculated air.
- the RECIRC button is disabled and the indicator is illuminated. (RECIRC forced ON)
- the defrost/panel/floor door directs airflow to the instrument panel A/C registers.
- blended air temperature is available.
- the A/C request button is illuminated and disabled.
- the A/C compressor operates if the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
PANEL
When PANEL is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator ON), the air inlet door actuator closes off outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator OFF), the air inlet door admits only outside air into the passenger compartment.
- the defrost/panel/floor door directs airflow to the instrument panel A/C registers.
- blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator ON), can the airflow temperature be cooled below the outside air temperature.
- the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
PANEL/FLOOR
When PANEL/FLOOR is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator ON), the air inlet door closes off outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator OFF), the air inlet door admits only outside air into the passenger compartment.
- the defrost/panel/floor door directs airflow to the floor duct and the instrument panel A/C registers. A small amount of airflow from the side window demisters and defrost duct is present.
- blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator ON), can the airflow temperature be cooled below the outside air temperature.
- the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
FLOOR
When FLOOR is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator ON), the air inlet door closes off outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator OFF), the air inlet door admits only outside air into the passenger compartment.
- the defrost/panel/floor door directs airflow to the floor duct. A small amount of airflow from the defroster duct and side window demisters is present.
- blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator ON), can the airflow temperature be cooled below the outside air temperature.
- the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
FLOOR/DEFROST
When the FLOOR/DEFROST is selected:
- the RECIRC request button is disabled. The air inlet door opens, admitting only outside air into the passenger compartment.
- the defrost/panel/floor door directs airflow to the floor duct, the defroster duct and the side window demisters.
- blended air temperature is available.
- the A/C request button is enabled. The A/C compressor operates automatically and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
DEFROST
When DEFROST is selected:
- the RECIRC request button and indicator is disabled. Regardless of button and indicator status, the air inlet door admits only outside air into the passenger compartment.
- the defrost/panel/floor door actuator directs airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct will be present.
- blended air temperature is available.
- the A/C request button indicates the last status and the indicator can be toggled. To reduce fogging, the A/C compressor operates automatically, regardless of indicator status, if the outside temperature is above approximately 0°C (32°F).
- the blower motor is ON.
Auxiliary Electric Heater
An auxiliary electric heater is available as optional equipment on diesel vehicles. The auxiliary electric heater assembly contains the Auxiliary Heater Control Module (AHCM) and element and is located in the heater core and evaporator core housing, immediately downstream of the heater core.
Power is supplied to the AHCM element through a fused cable connected directly to the positive battery terminal with an in-line connection at the dash panel heater tube opening. Ground is supplied to the electric heater element through a ground cable connected directly to the negative battery terminal with an in-line connection at the dash panel heater tube opening. The AHCM is activated by a Medium Speed Controller Area Network (MS-CAN) message from the HVAC module. The MS-CAN message is converted to a High Speed Controller Area Network (HS-CAN) message by the Instrument Cluster (IC) module and is then detected by the AHCM.
The auxiliary electric heater activates if all of the following conditions are met:
- The ignition switch is in the RUN/START position
- The engine is operating at greater than 500 rpm
- Any ON mode is selected on the HVAC module
- The temperature setpoint is greater than 80% of the highest setting (Electronic Manual Temperature Control (EMTC) only, DATC uses software algorithm based on interior temp and set point)
- The engine coolant temperature is less than 85°C (185°F)
- No alternator faults have been recorded and alternator is not at full capacity
The AHCM deactivates if any of the following conditions are met:
- The ignition switch is in the OFF or ACC position
- The engine coolant temperature is greater than 85°C (185°F)
- An alternator fault has been detected or the alternator is fully loaded due to external electrical loads
- The engine is operating at less than 500 rpm
- The auxiliary heat request is NO from the HVAC module - EMTC or HVAC module - Dual Automatic Temperature Control (DATC)