The Refrigerant Cycle

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 EMTC system:

The PCM controls the A/C clutch relay.

The evaporator temperature sensor monitors the temperature of the evaporator core and sends a signal to the PCM. If the temperature of the evaporator core 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 capacity may vary and may be 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

Courtesy of FORD MOTOR COMPANY

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 (Air Conditioning) Request

When an A/C request is received by the PCM, the PCM engages the A/C clutch relay when all 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 4°C (39°F).
Wide Open Throttle (WOT) condition is not present.
Evaporator temperature is above approximately 5°C (41°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 (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°C (32.4°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. For more information on PCM sensors, Refer to ENGINE CONTROLS - INTRODUCTION (EXCEPT DIESEL & HYBRID) .

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 door, which regulates 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.

Sensor Inputs

The evaporator temperature sensor is an input to the HVAC control module and the information is relayed to the PCM over the CAN. The Ambient Air Temperature (AAT) sensor is an input to the PCM. The PCM sends the Ambient Air Temperature (AAT) sensor information to the HVAC control module. If the temperatures are below a predetermined value, the PCM does not allow the A/C clutch to engage.

Air Handling

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

Air distribution
Air inlet
Temperature

The 2 circuit type Air inlet door actuator contains only a reversible electric motor. The 5 circuit type Air Inlet, Air distribution and Temperature door actuators contain a reversible electric motor and a potentiometer. The potentiometer circuits consist 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 (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 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.

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 admits only recirculated air.
the recirculated air indicator is illuminated (recirculated air forced on).
the mode doors 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 4°C (39°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 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.
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 mode doors direct airflow to the floor duct and the instrument panel registers. A small amount of airflow from the defroster duct and side window demisters is present.
blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
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 mode doors 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. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
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 mode doors direct airflow to the floor duct, the defroster duct and the side window demisters.
blended air temperature is available.
the A/C request button toggles the indicator on and off. To reduce fogging, the A/C compressor operates automatically, regardless of indicator status, if the outside temperature is above approximately 4°C (39°F).
the blower motor is on and the speed is adjustable.

DEFROST

When DEFROST is selected:

the recirculated air request button is disabled. The air inlet door opens, allowing only outside air into the passenger compartment.
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 A/C is on in defrost. The A/C compressor operates as long as the outside temperature is above approximately 4°C (39°F).
blended air temperature is available.
the blower motor is on and the speed is adjustable.