Climate Control System - Vehicles With: Electronic Manual Temperature Control (EMTC) - System Operation and Component Description

System Operation

System Diagram

Network Message Chart

  Module Network Input Messages PCM

  Module Network Input Messages FCIM

The Refrigerant Cycle

NOTE: HEV (hybrid electric vehicle) shown, others similar.

During stabilized conditions ( A/C system shutdown), the refrigerant pressures are equal throughout the system. When the A/C compressor is in operation, it increases refrigerant vapor pressure, raising its temperature. The high-pressure and high-temperature vapor is then released into the top of the A/C condenser core.

The A/C condenser, being close to ambient temperature, causes the refrigerant vapor to condense into a liquid when heat is removed from the refrigerant by ambient air passing over the fins and tubing. The now liquid refrigerant, still at high pressure, exits from the bottom of the A/C condenser and enters the inlet side of the A/C receiver/drier (integral to the condenser). The receiver drier is designed to remove moisture from the refrigerant system.

The outlet of the receiver drier is connected to the Thermostatic Expansion Valve (TXV). The Thermostatic Expansion Valve (TXV) provides the orifice, restricting refrigerant flow and separating the high and low pressure sides of the A/C system. As the liquid refrigerant passes across this restriction, its pressure and boiling point are reduced.

The liquid refrigerant is now at its lowest pressure and temperature. As it passes through the A/C evaporator, it absorbs heat from the airflow passing over the plate/fin sections of the A/C evaporator. This addition of heat causes the refrigerant to boil (convert to gas). The now cooler air can no longer support the same humidity level of the warmer air and the excess moisture condenses on the exterior of the evaporator coils and fins and drains outside the vehicle.

The refrigerant cycle is now repeated with the A/C compressor again increasing the pressure and temperature of the refrigerant.

The PCM monitors the evaporator temperature sensor thermistor as air is passed through the evaporator core and controls the A/C clutch relay. If the temperature of the evaporator core is low enough to cause the condensed water vapor to freeze, the A/C clutch is disengaged by the PCM .

The high-side line pressure is monitored so that A/C compressor operation is interrupted if the system pressure becomes too high or too low (low charge condition).

The A/C compressor pressure relief valve opens and vents refrigerant to relieve unusually high system pressure.

Control System Logic

When the customer directly inputs an A/C request into the FCIM , the module sends the request to the GWM over the Medium Speed Controller Area Network (MS-CAN). The GWM sends the request to the PCM over the High Speed Controller Area Network (HS-CAN). The PCM controls the A/C clutch relay.

The FCIM Programmable Module Installation (PMI) when it is replaced.

Controls and Compressor Operation

When an A/C request is received by the PCM , the PCM engages the A/C clutch relay when all of the following conditions are met:

• The PCM does not detect excessively high or low refrigerant pressure from the A/C pressure transducer.
• The PCM does not detect an ambient air temperature below approximately 35.6 °F ( 2 °C).
• The PCM does not receive a message from the FCIM detecting an evaporator temperature below approximately 35.6 °F ( 2 °C).

The PCM monitors the discharge pressure measured by the A/C pressure transducer. The PCM interrupts A/C compressor operation in the event the A/C pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM does not allow the A/C clutch to engage.

The FCIM adjusts the air inlet door depending on the humidity measured by the in-vehicle temperature and humidity sensor. If the vehicle cabin becomes too humid and recirculated air is selected, the FCIM adjusts the air inlet door to allow more fresh air. When the humidity level drops, it may adjust back to partial recirculated air. The FCIM also adjusts the system based on in-vehicle temperature.

Heating and Ventilation

The heating and ventilation system:

• controls the temperature of the air inside the vehicle.
• reduces the relative humidity of the air inside the vehicle (during A/C compressor operation).
• delivers heated or cooled air to maintain the vehicle interior temperature and comfort level.

Vehicles equipped with Auto Start-Stop have a cabin heater coolant pump.

Air Handling

There are 3 door actuators that control the air flow into the passenger compartment:

• Air distribution
• Air inlet
• Passenger side temperature

All of the door actuators contain a reversible electric motor and a potentiometer. The potentiometer circuit consists of a 5-volt reference signal connected to one end of a variable resistor, and a signal ground connected to the other. A signal circuit is connected to a contact wiper, which is driven along the variable resistor by the actuator shaft. The signal to the FCIM from the contact wiper indicates the position of the actuator door. The FCIM powers the actuator motors to move the doors to the desired positions. The desired door positions are calculated by the FCIM based on the set temperature, in-vehicle temperature, ambient air temperature and sunload.

When an airflow mode, desired temperature, fresh air, or recirculation mode is selected, the FCIM moves the actuator motor in the desired direction.

The FCIM sends a PWM signal to the blower motor speed control to regulate the blower speed as necessary. The blower motor speed control provides variable ground feed for the blower motor based on the input from the FCIM . A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

OFF

When OFF is selected:

• the air inlet door closes, preventing outside air and allowing only recirculated air.
• the blower motor is off.

MAX AC

When MAX A/C is selected:

• the air inlet door closes, preventing outside air and allowing only recirculated air.
• the recirculated air indicator is illuminated (recirculated air forced on).
• the footwell vent doors and defrost vent/register doors operate in combination to direct airflow to the instrument panel registers.
• the temperature door moves to the full cool position. Air temperature can be manually overridden.
• the A/C button is illuminated.
• the A/C compressor operates if the outside temperature is above approximately 35.6 °F ( 2 °C) .
• the blower motor is commanded to the highest speed. The blower motor speed is adjustable.

PANEL

When PANEL mode is selected:

• the recirculated air request button is enabled. If the recirculated air request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the recirculated air request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the footwell vent doors and defrost vent/register doors operate in combination to direct airflow to the instrument panel registers.
• blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C button (indicator on) can the airflow temperature be cooled below the outside air temperature.
• the blower motor is on and the speed is adjustable.

PANEL-FLOOR

When PANEL/FLOOR mode is selected:

• the recirculated air request button is enabled. If the recirculated air request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the recirculated air request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the air distribution doors operate in combination to direct airflow to the floor duct and the instrument panel 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 button (indicator on) can the airflow temperature be cooled below the outside air temperature.
• the blower motor is on and the speed is adjustable.

FLOOR

When FLOOR mode is selected:

• the recirculated air request button is enabled. If the recirculated air request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the recirculated air request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the air distribution doors operate in combination to direct 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 button (indicator on) can the airflow temperature be cooled below the outside air temperature.
• the blower motor is on and the speed is adjustable.

FLOOR-DEFROST

When FLOOR/DEFROST mode is selected:

• the recirculated air request button is enabled. If the recirculated air request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the recirculated air request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the air distribution doors operate in combination to direct airflow to the floor duct, the defroster duct and the side window demisters.
• blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C button (indicator on) can the airflow temperature be cooled below the outside air temperature.
• the blower motor is on and the speed is adjustable.

MAX DEFROST

When MAX DEFROST mode is selected:

• The recirculated air request button is disabled. The air inlet door opens, allowing only outside air into the passenger compartment.
• The air distribution doors operate in combination to direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
• The A/C is turned on in defrost mode. The A/C compressor operates as long as the outside temperature is above approximately 35.6 °F ( 2 °C).
• The temperature is set to the highest setting and is not adjustable.
• The fan is set to the highest speed and is not adjustable.
• MAX DEFROST can be exited by pressing the AUTO button.

Remote Start

Remote start is an optional feature available on this vehicle. In addition to being able to start the vehicle remotely, the remote start feature also utilizes other vehicle systems to increase the level of comfort to the vehicle occupants upon entering the vehicle. Additional information on the remote start feature and the other vehicle systems, refer to Owner's Literature.

When the factory remote start feature is used, the EMTC system runs at the setting it was set to when the vehicle was last turned off. You cannot adjust the climate control system during remote start operation. Turn the ignition on to return the system to its previous settings.

Set the climate control to operate using the last climate control settings through the information display setting: Remote Start > Climate Control > Heater–A/C > Last Settings, refer to the Owner's Literature for more information.

Component Description

FCIM - Electronic Manual Temperature Control (EMTC)

The EMTC system uses the FCIM as the HVAC control module. The FCIM also controls the outputs for rear window defrost and climate controlled seats. For details on the FCIM communication, refer to Control System Logic in this section.

The FCIM utilizes a Field-Effect Transistor (FET) protective circuit strategy for its actuator outputs. Output load (current level) is monitored for excessive current (typically short circuits) and is shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A short circuit DTC is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the Field-Effect Transistor (FET) circuit protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short (Field-Effect Transistor (FET) protection) and the circuit is still shorted, the Field-Effect Transistor (FET) protection shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. The Field-Effect Transistor (FET) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the Field-Effect Transistor (FET) and the ability of the Field-Effect Transistor (FET) to withstand it. A module lifetime level of fault events is established based upon the durability of the Field-Effect Transistor (FET). If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, the short circuit DTC that was stored on the first failure cannot be cleared by a command to clear the Diagnostic Trouble Codes (DTCs). The module does not allow the DTC to be cleared or the circuit to be restored to normal operation until a successful self-test proves that the fault has been repaired. After the self-test has successfully completed (no on-demand Diagnostic Trouble Codes (DTCs) present), DTC U1000:00 and the associated DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.

When each level is reached, the DTC associated with the short circuit sets along with DTC U1000:00. These Diagnostic Trouble Codes (DTCs) can be cleared using the module self-test, then the Clear DTC operation on the scan tool. The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur.

If the number of short circuit fault events reach the third level, then Diagnostic Trouble Codes (DTCs) U1000:00 and U3000:49 set along with the associated short circuit DTC . DTC U3000:49 cannot be cleared and a new module must be installed after the repair.

The FCIM requires Programmable Module Installation (PMI) when it is replaced.

Cabin Heater Coolant Pump

The cabin heater coolant pump is available on vehicles equipped with Auto Start-Stop feature only. The cabin heater coolant pump provides coolant to the heater core whenever the HVAC system requests heat and the vehicle is in Auto Start-Stop mode. Refer to the Owner's Literature, Unique Driving Characteristics, for full Auto Start-Stop enabling/disabling information.

The PCM sends a PWM signal to the cabin heater coolant pump based upon the:

• Auto Start-Stop mode enabled
• HVAC system temperature control setting (requesting heat)
• Ambient air temperature
• Engine coolant temperature
• Engine Revolutions Per Minute (RPM)
• Vehicle speed

Blower Motor

The blower motor pulls air from the air inlet and forces it into the heater core and evaporator core housing and the plenum chamber where it is mixed and distributed.

Blower Motor Speed Control

The blower motor speed control uses a PWM signal from the FCIM to determine the desired blower speed and varies the ground feed for the blower motor to control the speed.

Evaporator Core

The evaporator core is an aluminum plate/fin type and is located in the heater core and evaporator core housing. A mixture of liquid refrigerant and oil enters the bottom of the evaporator through the evaporator inlet tube and continues out of the evaporator through the evaporator outlet tube as a vapor. During A/C compressor operation, airflow from the blower motor is cooled and dehumidified as it flows through the evaporator fins.

Heater Core

The heater core consists of fins and tubes arranged to extract heat from the engine coolant and transfer it to air passing through the heater core.

Heater Core and Evaporator Core Housing

The heater core and evaporator core housing directs airflow from the blower motor through the evaporator core and heater core. All airflow from the blower motor passes through the evaporator core. The airflow is then directed through or around the heater core by the temperature door(s). After passing through the heater core, the airflow is distributed to the selected outlet by the airflow mode doors.

Air Distribution Door Actuator

The air distribution door actuator contains a reversible electric motor and a potentiometer. The potentiometer allows the FCIM to monitor the position of the airflow mode door.

Air Inlet Door Actuator

The air inlet door actuator contains a reversible electric motor and a potentiometer. The potentiometer allows the FCIM to monitor the position of the airflow mode door. The FCIM drives the actuator motor in the direction necessary to move the door to the position set by the recirculation button and the in-vehicle temperature and humidity sensor information.

Passenger Side Temperature Door Actuator

The EMTC system has one temperature door actuator located on the passenger side of the HVAC case. The passenger side temperature door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the FCIM to monitor the position of the temperature blend door.

Evaporator Temperature Sensor

The evaporator temperature sensor contains a thermistor. The sensor varies its resistance with the temperature. As the temperature rises, the resistance falls. As the temperature falls, the resistance rises. The evaporator temperature sensor is an input to the FCIM and the information is relayed to the PCM over the CAN . If the temperature is below a predetermined value, the PCM does not allow the A/C compressor to operate.

In-Vehicle Temperature And Humidity Sensor

The in-vehicle temperature and humidity sensor contains a thermistor and a sensing element which separately measures the in-vehicle air temperature and the humidity, then sends those readings to the FCIM . The in-vehicle temperature and humidity sensor has an electric fan within the sensor that draws in-vehicle air across the two sensing elements. The FCIM may adjust the air inlet door based on the in-vehicle temperature and humidity sensor information to maintain the desired humidity of the passenger cabin air.

Air Conditioning (A/C) Pressure Transducer

The PCM monitors the discharge pressure measured by the A/C pressure transducer. As the refrigerant pressure changes, the resistance of the A/C pressure transducer changes. It is not necessary to recover the refrigerant before removing the A/C pressure transducer.

Driver Side Footwell Air Discharge Temperature Sensor

The driver side footwell air discharge temperature sensor is an input to the FCIM . The driver side footwell air discharge temperature sensor contains a thermistor. The sensor varies its resistance with the temperature. As the temperature rises, the resistance falls. As the temperature falls, the resistance rises. The FCIM uses the sensor information to maintain the desired temperature of the passenger cabin air.

Internal Heat Exchanger (IHX)

The evaporator inlet and outlet manifold incorporates the Internal Heat Exchanger (IHX) and is serviced as an assembly. The Internal Heat Exchanger (IHX) combines a section of the A/C suction and liquid refrigerant lines into one component. It uses the cold vapor from the evaporator to cool the hot liquid from the condenser before it enters the Thermostatic Expansion Valve (TXV). After the Thermostatic Expansion Valve (TXV), more liquid refrigerant is available for absorbing heat in the evaporator. The result is an increase in cooling and operating efficiency of the HVAC system.

Externally Controlled Variable Displacement A/C Compressor

The externally controlled variable displacement compressor has:

• a non-serviceable shaft seal.
• a non-serviceable pressure relief valve installed in the rear of the compressor to protect the refrigerant system against excessively high refrigerant pressures.
• a non serviceable A/C clutch and field coil.
• Uses Polyalkylene Glycol (PAG) oil or equivalent. This oil contains special additives required for the A/C compressor. The oil may have some slightly dark-colored streaks while maintaining normal oil viscosity. This is normal for this A/C compressor because of break-in wear that can discolor the oil.

Variable displacement compressors have a swash plate that rotates to reciprocate pistons, which compresses refrigerant. Variable displacement compressors change the swash plate angle to change the refrigerant displacement. The externally controlled variable displacement compressor changes the swash plate angle in accordance with an electrical signal from the PCM . Externally controlled variable displacement compressor manages displacement by controlling refrigerant differential pressure before and after a throttle at the discharge side; achieving precise cooling capability control in accordance with cabin environment and driving conditions.

The PCM sends a PWM signal to the solenoid in the compressor to control the compressor displacement based upon the:

• Evaporator temperature
• Ambient air temperature
• Engine Revolutions Per Minute (RPM)
• Vehicle speed
• A/C high side pressure
• Intake air temperature

Condenser

The A/C condenser is an aluminum fin-and-tube design heat exchanger. It cools compressed refrigerant gas by allowing air to pass over fins and tubes to extract heat, and condenses gas to liquid refrigerant as it is cooled. The receiver/drier is integral to the A/C condenser.

Integrated Receiver Drier

The integrated receiver drier stores high-pressure liquid and the desiccant bag mounted inside the receiver drier removes any retained moisture from the refrigerant.

The receiver drier element is incorporated onto the LH side of the A/C condenser. The receiver drier element can be separately removed and installed with the A/C condenser in the vehicle.

Thermostatic Expansion Valve (TXV)

The Thermostatic Expansion Valve (TXV) is located at the evaporator core inlet and outlet tubes at the center rear of the engine compartment. The TXV provides a restriction to the refrigerant flow and separates the low-pressure and high-pressure sides of the refrigerant system. Refrigerant entering and exiting the evaporator core passes through the TXV through 2 separate flow paths. An internal temperature sensing bulb senses the temperature of the refrigerant flowing out of the evaporator core and adjusts an internal pin-type valve to meter the refrigerant flow into the evaporator core. The internal pin-type valve decreases the amount of refrigerant entering the evaporator core at lower temperatures and increases the amount of refrigerant entering the evaporator core at higher temperatures.

Service Gauge Port Valves

The service gauge port fitting is an integral part of the refrigerant line or component.

• Prior to leak testing, blow air over service gauge port valves to insure an accurate test.
• Special couplings are required for both the high-side and low-side service gauge ports.
• A very small amount of leakage is always detectable around the Schrader-type valve with the service gauge port valve cap removed, and is considered normal. A new Schrader-type valve core can be installed if the seal leaks excessively.
• The A/C service gauge port valve caps are used as primary seals in the refrigerant system to prevent leakage through the Schrader-type valves from reaching the atmosphere. Always install and tighten the A/C service gauge port valve caps to the correct torque after they are removed.
• Follow the procedure and the notes for electronic leak testing. Refer to:
  Refer to: Electronic Leak Detection (412-00 Climate Control System - General Information, General Procedures).
  

Refrigerant System Dye

A fluorescent refrigerant system dye wafer is added to the receiver drier desiccant bag to assist in refrigerant system leak diagnosis using a Rotunda-approved UV blacklight. This fluorescent dye wafer dissolves after about 30 minutes of continuous A/C operation. It is not necessary to add additional dye to the refrigerant system before diagnosing leaks, even if a significant amount of refrigerant oil has been removed from the system.

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