The Refrigerant Cycle: Notes
For information regarding basic HVAC (heating, ventilation and air conditioning) 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 / EATC 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 A/C clutch is disengaged by the PCM.
- 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.
| Item | Description |
|---|---|
| 1 | High pressure liquid |
| 2 | Low pressure liquid |
| 3 | High pressure vapor |
| 4 | Low pressure vapor |
Control System Logic
When the customer directly inputs an A/C request into the HVAC control module, the module sends the request to the GWM over the MS-CAN. The GWM relays the request to the PCM over the HS-CAN1. The PCM controls the A/C clutch relay.
A/C Request
When the A/C is requested, the HVAC control module sends the message over the MS-CAN to the GWM. The GWM sends the A/C request through the HS-CAN to the PCM.
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.
- Ambient air temperature is above approximately 0deg.C (32deg.F).
- Engine coolant temperature conditions are within normal parameters.
- Wide Open Throttle (WOT) condition is not present.
- Evaporator temperature is above approximately 1deg.C (33.8deg.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 of 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 18 deg.C (64.4 deg.F). If a temperature sensor input is found to be reporting a temperature imbalance the PCM does not allow the A/C clutch to engage.
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 HVAC control module adjusts the system based on cabin temperature. If equipped with the in-vehicle and humidity sensor, the HVAC control module also 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 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.
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 the 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.
Air Handling
There are 3 door actuators that control the EATCHVAC system air flow into the passenger compartment:
- Air distribution
- Air inlet
- Temperature door actuator
There are 4 door actuators that control the DATCHVAC system air flow into the passenger compartment:
- Air distribution
- Air inlet
- Driver side temperature
- 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 HVAC control module from the contact wiper indicates the actuator door position. 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 (if equipped the in-vehicle temperature and humidity sensor), and ambient air temperature.
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 sends a PWM signal to the blower motor control module to regulate the blower speed as necessary. The blower motor control module 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.
Air Flow Strategy For Anti Fogging
This vehicle is equipped with an anti fogging feature known as enhanced windshield anti fogging strategy (EWAFS). This feature is based off the input data that is sent from the in-vehicle temperature and humidity sensor that is mounted near the center top of the windshield typically under the IPMA cover. The in-vehicle temperature and humidity sensor is hard wired to the HVAC module and supplies the vehicles humidity and temperature to the HVAC module. The module uses that data automatically to adjust the airflow in the cabin to prevent the windshield from fogging up. Below are the feature details and climate control operation based on the vehicles climate control system.
| Background Strategy Operations | ||
|---|---|---|
| Background Feature Details | Single Zone Manual | Dual Zone/Single Zone Auto |
| To prevent window fogging, recirculated air cannot be switched on when MAX Defrost is on. | X | X |
| In certain conditions (i.e. Max Defrost), the A/C compressor may continue to operate even though the A/C button is off. | X | X |
| In certain conditions, the A/C button may turn on and off automatically based on the temperature setting and/or the current conditions. | X | X |
| Recirculated air may turn off automatically (or be prevented from turning on) in all airflow modes except MAX A/C to reduce risk of fogging. Recirculated air may also turn on and off automatically in various airflow modes in order to improve heating or cooling efficiency. | X | X |
| Whenever the blower motor speed is automatically controlled, all of the blower indicators turn off. | - | X |
| When Auto operation is switched on the air distribution, A/C operation, and outside or recirculated air will also be automatically controlled to heat or cool the vehicle in order to maintain the selected temperature. Under high humidity conditions, automatic operation will also take action to reduce the risk of window fogging by automatically engaging the A/C compressor, increasing blower motor speed, and/or directing more air to the windshield. | - | X |
AUTO
When AUTO is selected:
- the HVAC system operates in a manner to achieve and maintain the temperature set by the operator.
- the air inlet door actuator is automatically controlled by the HVAC module based on the temperature setting.
- the mode door actuator is automatically controlled by the HVAC module based on the temperature setting.
- the temperature door is automatically controlled by the HVAC module based on the temperature setting.
- the A/C compressor is automatically controlled by the HVAC control module based on the temperature setting. The A/C compressor does not operate if the outside temperature is below approximately 4 deg.C (39 deg.F).
- the blower motor speed is automatically controlled through the blower motor speed control when it receives a PWM signal from the HVAC control module based on the temperature setting, but can be manually adjusted if desired.
OFF
When the system is OFF:
- 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 mode is selected:
- the air distribution doors operate simultaneously to direct airflow to the instrument panel registers. A small amount of airflow from the floor duct is present.
- the temperature door moves to the full cool position.
- the blower motor is commanded to the highest speed, but can be manually adjusted if desired.
- the air inlet door closes, preventing outside air and admits only recirculated air.
- the recirculated air indicator is illuminated (recirculated air forced on).
- the A/C button is illuminated.
- the A/C compressor operates if the outside temperature is above approximately 2deg.C (35.6deg.F).
PANEL
When PANEL mode is selected:
- the mode doors direct airflow to the instrument panel registers.
- the recirculated air request button can be enabled.
- blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
PANEL-FLOOR
When PANEL-FLOOR mode is selected:
- the mode doors 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.
- the recirculated air request button can be enabled.
- blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
FLOOR
When FLOOR is selected:
- the mode doors direct airflow to the floor duct. A small amount of airflow from the defroster duct and side window demisters is present.
- the recirculated air request button can be enabled.
- blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
FLOOR-DEFROST
When FLOOR-DEFROST is selected:
- the mode doors direct airflow to the floor duct, the defroster duct and the side window demisters.
- the recirculated air request button can be enabled, but can automatically turn off.
- blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
DEFROST
When DEFROST is selected:
- the mode doors direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
- the recirculated air request button can be enabled, but can automatically turn off.
- the A/C is automatically commanded on and remains on until the system is either turned off or the airflow mode has changed and the A/C button is pressed.
- the A/C compressor operates as long as the outside temperature is above approximately 2deg.C (35.6deg.F).
MAX DEFROST
When MAX DEFROST 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 automatically commanded on and remains on until the system is either turned off or the airflow mode has changed and the A/C button is pressed.
- the A/C compressor operates as long as the outside temperature is above approximately 2deg.C (35.6deg.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.
Cowl Pressure Blower Motor Strategy
When the climate system is in outside air mode (air entering the cowl air inlet), the air pressure increases as vehicle speed increases. The change in pressure is a function of vehicle shape. The change in pressure effectively changes the airflow into the vehicle.
If the vehicle is equipped with EATC, there are calibration strategies that help reduce the effect of cowl pressure. The blower motor slows down to offset increased cowl pressure as the vehicle speed increases until it reaches minimum voltage. However, for vehicles with a high cowl pressure effect, the changes in airflow may still be perceived by the customer. If the HVAC has a variable outside air inlet door (such as the Mustang Mach-E), then the EATC can control the cowl pressure to reduce the airflow entering the vehicle.
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 DATC system runs at the setting it was set to when the vehicle was last turned off. 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. The climate control system automatically uses the settings last selected before the vehicle was turned off. Refer to the Owner's Literature for more information.