Ford Explorer: Climate Control System - General Information / Description and Operation - Climate Control System - System Operation and Component Description

Ford Explorer 2020-2022 Service Manual / Electrical / Climate Control System / Climate Control System - General Information / Description and Operation - Climate Control System - System Operation and Component Description

System Operation

System Diagram


Item Description
1 Hybrid
2 FDIM
3 Microphone
4 APIM
5 GWM
6 A/C clutch relay
7 Sunload sensor
8 FCIM-B
9 BCM
10 Ambient air quality sensor (if equipped)
11 SOBDMC
12 ACCM
13 Ambient Air Temperature (AAT) sensor
14 A/C compressor clutch field coil
15 Externally Controlled Variable Displacement (EVDC) compressor
16 In-vehicle temperature and humidity sensor
17 Evaporator temperature sensor
18 HVAC control module
19 Air distribution door actuator
20 Driver temperature door actuator
21 Passenger temperature door actuator
22 Air inlet door actuator
23 Blower motor relay
24 Blower motor control module
25 Driver side register air discharge temperature sensor
26 Driver side footwell air discharge temperature sensor
27 Passenger side footwell air discharge temperature sensor
28 Passenger side register air discharge temperature sensor
29 A/C pressure transducer
30 Cabin heater coolant pump
31 PCM

Network Message Chart

  Module Network Input Messages - ACCM


Broadcast Message Originating Module Message Purpose
Ambient air temperature filtered PCM \ PCM_HEV This message contains the climate control system controls ambient air temperature information.

  Module Network Input Messages - APIM


Broadcast Message Originating Module Message Purpose
Climate control button status   HVAC This message contains the climate control button status.
Climate control temperature display   HVAC This message contains the HVAC temperature setting.
Front blower indicator   HVAC This message contains the HVAC blower motor setting for the touch screen display.
Temperature unit selection HVAC control module This message contains the IPC temperature setting.
HVAC front blower indicator HVAC control module This message contains the HVAC blower motor setting.
Outside Air Temperature HVAC control module This message contains the Ambient Air Temperature information for the FDIM touchscreen outside air temperature display.

  Module Network Input Messages - FCIMB


Broadcast Message Originating Module Message Purpose
Climate control touchscreen and voice requests   APIM This message contains both the climate control system voice commands as well as all climate control system touchscreen inputs.
Climate control status HVAC control module This message contains the HVAC mode status for the mode indicators.

  Module Network Input Messages - HVAC control module


Broadcast Message Originating Module Message Purpose
Remote start status   BCM This message contains the climate control system controls request for remote start.
A/C clutch status   PCM This message contains the A/C compressor clutch status.
Ambient air temperature   PCM This message contains raw value from the ambient temperature sensor.

  Module Network Input Messages - PCM


Broadcast Message Originating Module Message Purpose
A/C request HVAC control module This message requests the A/C compressor to be engaged.
Evaporator temperature HVAC control module This message contains the evaporator temperature. The PCM uses the evaporator temperature to determine the A/C compressor output.
HVAC remote start request HVAC control module This message contains the climate control system controls for ambient air temperature information.

The Refrigerant Cycle (Non-Hybrid)

For information regarding basic HVAC system refrigerant operation, refer to the current Ford Web Based Technical Training courses. The following diagram shows the refrigerant system state in each component.

The following are characteristics of the DATC system:

  • The PCM controls the A/C clutch relay.
  • The evaporator temperature sensor monitors the temperature of the air that has passed through the evaporator core and sends a signal to the PCM. If the temperature of the evaporator core discharge air is low enough to cause the condensed water vapor to freeze, the PCM disengages the A/C clutch relay.
  • The line pressure is monitored so that A/C compressor operation is interrupted if the system pressure becomes too high or too low.
  • The A/C compressor relief valve opens and vents refrigerant to relieve unusually high system pressure.

A/C Flow and State (2.3L EcoBoost)

Item Description
1 High pressure liquid
2 Low pressure liquid
3 High pressure vapor
4 Low pressure vapor

A/C Flow and State (3.0L EcoBoost)

Item Description
1 High pressure liquid
2 Low pressure liquid
3 High pressure vapor
4 Low pressure vapor

A/C Flow and State (3.3L Duratec-V6)

Item Description
1 High pressure liquid
2 Low pressure liquid
3 High pressure vapor
4 Low pressure vapor

Control System Logic (Non-Hybrid)

The DATC system controls are in one or more locations depending on vehicle option content:

  • Front Controls Interface Control Module B (FCIM-B)
  • Touchscreen FDIM (part of APIM)

When the FDIM touchscreen or voice commands are used and A/C is selected, the APIM sends the request message over the HS-CAN3 to the GWM. The GWM sends the request to the PCM over the HS-CAN1. The PCM controls the A/C clutch relay. The GWM also sends the request to the HVAC control module over the MS-CAN.

When the customer inputs an A/C request into the Front Controls Interface Control Module B (FCIM-B), the module sends the request to the GWM over the HS-CAN3. The GWM sends the request to the PCM over the HS-CAN1. The PCM controls the A/C clutch relay. The GWM also sends the request to the HVAC control module over the MS-CAN.

A/C Request (Non-Hybrid)

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:

  • Excessively high or low refrigerant pressure from the A/C pressure transducer is not detected.
  • Engine coolant temperature conditions are within normal parameters.
  • Ambient air temperature is above approximately 0°C (32.0°F).
  • Wide Open Throttle (WOT) condition is not present.
  • Evaporator temperature is above approximately 2°C (35.6°F).
  • Engine torque conditions are within normal parameters.
  • Battery state of charge conditions are within normal parameters.

Compressor control and the evaporator temperature are a function of many parameters, not just a straight on/off, to avoid freezing the evaporator. The PCM monitors multiple temperature sensors for correlation including, but not limited to, AAT, CACT, CHT, ECT, IAT, IAT2, MAF, MAPT, TCB and TCIPT Parameter Identifications (PIDs) (as applicable). The PCM runs this logic after an engine off and a calibrated soak period, typically 6 to 8 hours. This soak period allows the Ambient Air Temperature (AAT) sensor and the other temperature sensors to stabilize and not differ by greater than a calibrated value, typically 18ºC (32.4ºF). If a sensor input is found to be reporting a temperature imbalance the PCM does not allow the A/C clutch to engage. For more information on PCM sensors, Refer to Powertrain Control/Emissions Diagnosis (PC/ED) manual.

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 Refrigerant Cycle (Hybrid)

For information regarding basic HVAC system refrigerant operation, refer to the current Ford Web Based Technical Training courses. The following diagram shows the refrigerant system state in each component.

The following are characteristics of the DATC system:

  • The SOBDMC sends the requests to the electric A/C compressor ACCM.
  • The evaporator temperature sensor monitors the temperature of the air that has passed through the evaporator core and sends a signal to the HVAC control module. If the temperature of the evaporator core discharge air is low enough to cause the condensed water vapor to freeze, a CAN message is sent to the ACCM to reduce the electric compressor output or shuts it off.
  • The line pressure is monitored through the pressure transducer so that the electric A/C compressor operation is interrupted if the system pressure becomes too high or too low.
  • The electric A/C compressor thermal protection switch interrupts compressor operation if the compressor housing exceeds temperature limits.
  • The A/C compressor relief valve opens and vents refrigerant to relieve unusually high system pressure.

A/C Flow and State (3.3L Duratec-V6-Hybrid (BP))

Item Description
1 High pressure liquid
2 Low pressure liquid
3 High pressure vapor
4 Low pressure vapor

Control System Logic (Hybrid)

The DATC system controls are in one or more locations depending on vehicle option content:

  • Front Controls Interface Control Module B (FCIM-B)
  • Touchscreen FDIM (part of APIM)

When the FDIM touchscreen or voice commands are used and A/C is selected, the APIM sends the request message over the HS-CAN3 to the GWM. When the customer inputs an A/C request into the Front Controls Interface Control Module B (FCIM-B), the module sends the request to the GWM over the HS-CAN3. Once the A/C request is selected from either interface, the GWM sends the request to the SOBDMC over the HS-CAN1. The SOBDMC controls the electric compressor. The GWM also sends the request to the HVAC control module over the MS-CAN.

A/C Request (Hybrid)

When the ACCM request for cooling, the electric A/C compressor is commanded on when all of the following conditions are met:

  • Excessively high or low refrigerant pressure from the A/C pressure transducer are not detected.
  • Ambient air temperature is above approximately 0°C (32.0°F).
  • Electric motor coolant temperature conditions are within normal parameters.
  • Evaporator temperature is above approximately 2°C (35.6°F).
  • Engine torque conditions are within normal parameters.
  • Battery state of charge conditions are within normal parameters.

Compressor control and the evaporator temperature are a function of many parameters, not just a straight on/off, to avoid freezing the evaporator. The PCM monitors multiple temperature sensors for correlation including, but not limited to, AAT, CACT, CHT, ECT, IAT, IAT2, MAF, MAPT, TCB and TCIPT Parameter Identifications (PIDs) (as applicable). The PCM runs this logic after an engine off and a calibrated soak period, typically 6 to 8 hours.

The PCM filters the ambient air temperature input and sends the data to the GWM through the HS-CAN1. The GWM sends the air ambient temperature filtered message to the HVAC control module over the MS-CAN.

This soak period allows the Ambient Air Temperature (AAT) sensor and the other temperature sensors to stabilize and not differ by greater than a calibrated value, typically 18ºC (32.4ºF). If a sensor input is found to be reporting a temperature imbalance the PCM does not allow the A/C clutch to engage. For more information on PCM sensors, Refer to Powertrain Control/Emissions Diagnosis (PC/ED) manual.

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 ACCM does not allow the electric A/C compressor to engage.

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

Rear Climate Control

For system operation and component description information on the rear climate control system,
Refer to: Rear Climate Control - System Operation and Component Description (412-02 Rear Climate Control, Description and Operation).

Supplemental Heating

For system operation and component description information on the supplemental heating climate control system,
Refer to: Supplemental Climate Control - System Operation and Component Description (412-03 Supplemental Climate Control, Description and Operation).

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.

The heating and ventilation system uses a reheat method to provide conditioned air to the passenger compartment. Temperature blending is controlled by temperature doors, which regulate the amount of air that flows through and around the heater core, where it is then mixed and distributed. All airflow from the blower motor passes through the A/C evaporator core.

Instrument Panel Console Switch Assembly - Auto Start-Stop Deactivation Switch (if equipped)

The Instrument Panel Console Switch Assembly - Auto Start-Stop deactivation switch is available on vehicles equipped with Auto Start- Stop feature only. Auto Start-Stop deactivation switch is a momentary contact switch that includes a LED indicator. This switch is used to deactivate the Auto Start-Stop mode. Refer to the Owner's Literature, Unique Driving Characteristics, for full Auto Start-Stop enabling/disabling information.

Cabin heat during an Auto Start-Stop operation

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.

Air Handling

There are 4 door actuators that control the air flow into the passenger compartment:

  • Air distribution
  • Air inlet
  • Driver temperature
  • Passenger 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 HVAC control module from the contact wiper indicates the position of the actuator door. The HVAC control module powers the actuator motors to move the doors to the desired positions. The desired door positions are calculated by the HVAC control module 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 HVAC control module moves the actuator motor in the desired direction.

The HVAC control module 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.

The HVAC control module 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 HVAC control module. A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

AUTO

When AUTO is selected:

  • the HVAC system operates in a manner to achieve and maintain the temperature set by the operator.
  • the driver and passenger side temperature doors are automatically controlled by the HVAC control module based on the temperature setting.
  • the A/C compressor is automatically controlled by the PCM from information sent by the HVAC control module, based on the temperature setting. The A/C compressor operates as long as the outside temperature is above approximately 0°C (32°F).
  • the blower motor speed is automatically controlled through the blower motor speed control that receives a PWM signal from the HVAC control module based on the temperature setting, but can be manually overridden.
  • the HVAC control module controls the air inlet door to recirculate, partially recirculate or open to the fresh air position depending on the in-car temperature and humidity sensor inputs.

OFF

When OFF is selected:

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

MAX A/C

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 doors move to the full cool position. Air temperature can be manually overridden.
  • the A/C button is illuminated.
  • the A/C compressor operates as long as the outside temperature is above approximately 0°C (32°F).
  • 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 0°C (32°F).
  • 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.

MyTemp

The MyTemp feature can be used to store and recall a preset driver's temperature. This feature is provided so this temperature can be quickly adjusted to a frequently used setting with a single button press. For additional information about MyTemp, refer to the Owner's Literature.

Remote Start - Message Center Set To Auto

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. For additional information on the remote start feature and the other vehicle systems, refer to the Owner's Literature.

Set the climate control to operate in Auto mode through the information display controls: Remote Start > Climate Control > Heater–A/C > Auto. The climate control system automatically sets the interior temperature to 72°F (22°C). Refer to the Owner's Literature for more information.

When the factory remote start feature is used, the DATC system automatically sets certain parameters in an attempt to achieve a comfortable cabin temperature. These parameters are set based on multiple inputs including the in-vehicle temperature and humidity, sunload and outside air temperature sensors.

Remote Start - Message Center Set To Last User Settings

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. For additional information on the remote start feature and the other vehicle systems, refer to the Owner's Literature.

Set the climate control to operate using the last climate control settings through the information display controls: Remote Start > Climate Control > Heater–A/C > Last Settings. The climate control system automatically uses the settings last selected before the vehicle was turned off. The climate control system cannot be adjusted during remote start operation. Turn the ignition on to return the system to its previous settings. Refer to the Owner's Literature for more information.

Component Description

A/C Electric Compressor

NOTE: Refer to Specifications in Group 412 for the appropriate refrigerant and refrigerant oil. The refrigerant and refrigerant oil listed are the only oils to be used as the refrigerant system lubricant for electric vehicles. Addition of any oil other than the referred to oils for the refrigerant system will damage the A/C electric compressor and contaminate the refrigerant system. Use the oil adding procedure specified for this vehicle when installing a new A/C electric compressor.

NOTE: For Hybrid Electric Vehicle (HEV) and Plug-In Hybrid Electric Vehicle (PHEV) vehicles, the A/C electric compressor may run and airflow may be felt when the climate control is off to provide cooling to the battery.

The ACCM is an integral part of the A/C electric compressor and cannot be removed from or serviced separately. The ACCM has both low voltage and high voltage connections. The ACCM requires a low voltage system operating voltage between 9 and 16 volts. The ACCM also requires high voltage system operating voltage between 110 and 467 volts. For diagnosis of the ACCM and A/C electric compressor,
Refer to: Climate Control System (412-00 Climate Control System - General Information, Diagnosis and Testing).

The A/C electric compressor allows for A/C operation to continue even when the vehicle is in full electric mode and the gasoline engine is not running.

Air Distribution Door Actuator

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

Air Discharge Temperature Sensors

There are 4 air discharge temperature sensors in the DATC system:

  • Driver side footwell air discharge temperature sensor
  • Driver side register air discharge temperature sensor
  • Passenger side footwell air discharge temperature sensor
  • Passenger side register air discharge temperature sensor

The air discharge temperature sensors contain a thermistor and are inputs to the HVAC control module. The sensors vary their resistance with the temperature. As the temperature rises, the resistance falls. As the temperature falls, the resistance rises. The HVAC control module uses the sensor information to maintain the desired temperature of the passenger cabin air.

Air Inlet Door Actuator

The air inlet door actuator contains a reversible electric motor and a potentiometer. The potentiometer allows the HVAC control module to monitor the position of the airflow mode door.

Ambient Air Quality Sensor (if equipped)

The ambient air quality sensor is an input to the HVAC control module. When pollution and bad odors coming from the external environment are detected, the air inlet door automatically closes.

Ambient Air Temperature Sensor

The Ambient Air Temperature (AAT) sensor is hardwired to the PCM through separate input and return circuits. The PCM provides a reference voltage to the Ambient Air Temperature (AAT) sensor and monitors the change in voltage resulting from changes in resistance as determined by outside air temperature.

After replacing an Ambient Air Temperature (AAT) sensor, the sensor data must be reset by either driving the vehicle at speeds consistently about 20 MPH for at least 5 minutes to update the filtered data or perform the multiple button press reset procedure to update to the current raw value.

The multiple button reset for the Ambient Air Temperature (AAT) sensor is as follows:

  • On the HVAC panel controls, press the A/C and Recirc buttons simultaneously for 5 seconds, then, release both, within 2 seconds press the A/C button again.

Blower Motor Control Module

The blower motor and the blower motor speed control are combined into one assembly called the blower motor control module. The blower motor pulls air from the air inlet and forces it into the climate control housing and the plenum chamber where it is mixed and distributed. The blower motor speed control uses a PWM signal from the HVAC control module to determine the desired blower speed and varies the ground feed for the blower motor to control the speed.

Cabin Heater Coolant Pump (if equipped)

The cabin heater coolant pump is utilized to circulate coolant though the vehicles cooling system based on certain vehicle demands. During low engine speeds the pump increases heater core flow that the main engine coolant pump provides. The specific RPM threshold varies based on the ambient and coolant temperatures. It also supplies coolant flow during an auto start - stop condition to maintain the cabin temperature when the cabin heat is turned on. The pump also turns on in response to high engine oil temperatures and increases the flow through the oil cooler to reduce the oil temperature. The pump is commanded on by the PCM.

Climate Control Housing

The climate control 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.

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.

Driver Temperature Door Actuator

The driver temperature door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC control module to monitor the position of the temperature door.

Evaporator Core

The evaporator core is an aluminum tube and fin design heat exchanger located in the climate control housing. A mixture of liquid refrigerant and oil enters through the evaporator core inlet tube and exits out of the evaporator core through the evaporator core 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 core fins.

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 HVAC control module and the information is relayed to the PCM over the CAN. If the evaporator temperature is below approximately 2°C (35.6°F), the PCM does not allow the A/C compressor to operate.

Externally Controlled Variable Displacement A/C Compressor

NOTE: Proper Air Conditioning (A/C) system diagnosis on a vehicle's compressor is dependent on correct refrigerant system charge and tested in ambient temperatures above 21.1°C (70°F).

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.
  • the appropriate compressor oil that 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 response to an electrical signal from the PCM. The 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 response to 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:

  • Ambient air temperature
  • Evaporator temperature
  • Engine RPM
  • Vehicle speed
  • A/C high side pressure
  • Temperature and mode settings of the climate control head
  • Intake air temperature

Heater Core

The heater core, located in the climate control housing, consists of fins and tubes arranged to extract heat from the engine coolant and transfer it to air passing through the heater core.

HVAC Control Module - Dual Automatic Temperature Control (DATC)

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

The HVAC control module utilizes a 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 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 ( FET protection) and the circuit is still shorted, the 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 FET protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET and the ability of the FET to withstand it. A module lifetime level of fault events is established based upon the durability of the 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 HVAC control module requires PMI when it is replaced.

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 HVAC control module. The HVAC control module 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.

Passenger Temperature Door Actuator

The passenger temperature door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC control module to monitor the position of the temperature door.

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.

A 5-volt reference voltage is supplied to the A/C pressure transducer from the PCM. The A/C pressure transducer receives a ground from the PCM. The A/C pressure transducer then sends a voltage to the PCM to indicate the A/C refrigerant pressure.

Receiver Drier

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

Sunload Sensor

The sunload sensor supplies information to the HVAC control module indicating the intensity of the sun on the vehicle. The HVAC control module compensates high sun load with higher blower and reduced discharge temperatures.

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

Item Description Torque
1 Low-pressure service gauge port valve cap 0.8 Nm (7 lb-in)
2 Low-pressure service gauge port valve
3 Low-pressure Schrader-type valve 1.8 Nm (16 lb-in)
4 High-pressure Schrader-type valve 2.5 Nm (22 lb-in)
5 High-pressure service gauge port valve
6 High-pressure service gauge port valve cap 0.8 Nm (7 lb-in)

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

  • Prior to leak testing, blow air over the service gauge port valves to ensure an accurate test.
  • Special couplings are required for both the high-side and low-side service gauge ports.
  • A very small amount of leakage around the Schrader-type valve with the service gauge port valve cap removed is considered normal. Install a new Schrader-type valve core 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 the appropriate Electronic Leak Detection procedure in General Procedures.

Refrigerant System Dye

A fluorescent dye wafer is added to the receiver drier desiccant bag at the factory to assist in refrigerant system leak diagnosis. 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 has been removed from the system.

Replacement desiccant bags, either separately or part of the receiver drier assembly, are equipped with a new fluorescent dye wafer. It is not necessary to add additional dye to the refrigerant system before diagnosing leaks. If the system has been out of refrigerant through the winter the dye at the leak point may have oxidized and may not fluoresce. If this happens, recharge and operate the A/C system to circulate the oil and allow any residual dye to show up at the leak point. It is important to understand that dye adheres to the oil not the refrigerant; the refrigerant carries the oil out of the leak point.

NOTE: Check for leaks using a Rotunda-approved UV lamp and dye enhancing glasses.

REFER to the appropriate Fluorescent Dye Leak Detection procedure in General Procedures.

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    Windshield Wipers

    Push the lever up or down to operate the windshield wipers.

    A - Single wipe.

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