The Refrigerant Cycle

For base operation regarding refrigerant operation within the HVAC system, please reference the current Ford Web Based Technical Training courses. The diagram below shows the states of the refrigerant in each component of the system for this vehicle. Please reference the diagram along with the training information for an understanding of the refrigerant cycle within this vehicle.

Some specific items to remember when working with this 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.

Thermostatic Expansion Valve (TXV) Type Refrigerant System State and Flow 

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 

The blower motor knob must be set to any speed other than 0 for the system to operate.

Controls and Compressor Operation 

All customer commands for the EMTC climate control system come through the HVAC control head.

A/C Request 

When the A/C button is pressed, the HVAC control module uses a dedicated wire to send the A/C request message to the BCM. The BCM 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:

• the refrigerant pressure is not excessively high or low.
• the engine coolant temperature is not excessively high.
• the ambient air temperature is above approximately 0°C (32°F).
• a WOT condition is not present.
• the evaporator discharge air temperature is above approximately 1°C (33.8°F).

Compressor Clutch 

When A/C is requested and A/C line pressures allow, a ground is provided to the A/C clutch relay coil from the PCM, energizing the A/C clutch relay. When the PCM energizes the relay, voltage is supplied to the A/C compressor clutch field coil from the relay.

Air Handling 

Based on the climate control system temperature settings, the temperature door actuator directs airflow through the evaporator and heater cores as needed. The air distribution door actuator controls the airflow to the defrost, floor or panel register vents. The air source is from outside air or recirculated passenger compartment air as determined by the air inlet door position. The air inlet door actuator contains a reversible electric motor with no potentiometer and is either fully open or fully closed.

The air distribution door and temperature door actuators are stepper motors. There is no feedback circuit or potentiometer for these actuators. The pins labeled Door A, B, C and D are for the different phases (coils) of the motor. All the phases for a given motor are fed from A/Common power lead, the pin labeled Door Power and the HVAC control module controls each phase by turning a low side output on or off for the different phases. The motor turns, or steps, through a series of motions to position the actuator. The HVAC control module tracks the actuator positions by counting steps and periodically calibrates itself so it knows how many steps there are for the full range movement of the actuator. The HVAC control module sets Diagnostic Trouble Codes (DTCs) by monitoring the current flow through a given phase. If it sees too much current it identifies it as a short circuit. If it does not see any current it identifies it as an open circuit.

The blower motor is controlled using a blower motor resistor. The blower motor resistor uses 3 resistance elements that are wired in series on the ground side of the blower motor. The blower motor has 4 speeds:

• for low speed, all 3 resistors are used
• for medium-low speed, resistors 1 and 2 are used
• for medium-high speed, resistor 1 is used
• for high speed, the blower motor is provided a path directly to ground and the blower motor resistors are not used

The HVAC control module grounds 1 of the 4 circuits to control the blower motor speed.

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 inlet door closes, preventing outside air and allowing 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 0°C (32°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 mode 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 mode 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 mode 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.