Controls and Compressor Operation

Climate Control Commands - A/C Request 

Climate control commands are input through the HVAC control module. On vehicles equipped with SYNC® system inputs can also be commanded through voice commands or the touch screen. When the A/C is requested, the HVAC control module sends the message over the MS-CAN 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 A/C clutch relay is engaged 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 32.0 °F (°C).
• Evaporator temperature is above approximately 33.8 °F (1 °C).
• Engine coolant temperature conditions are within normal parameters.
• Wide Open Throttle (WOT) condition is not present.
• 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, MAF, MAP, and MAPT (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 - Description & Operation (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.

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 

Based on the climate control system temperature settings, the temperature door actuators direct airflow through the evaporator and heater cores as needed. The air distribution door actuators control 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 defrost, panel-floor, air inlet 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 HVAC control module sends a PWM signal to the blower motor control module to control the blower motor speed. The blower motor control module provides variable ground feed for the blower motor. 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 air inlet door is automatically controlled by the HVAC control module based on the temperature setting.
• the mode door is automatically controlled by the HVAC control module based on the temperature setting.
• the temperature blend door is automatically controlled by the HVAC control 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 0°C (32°F).
• the blower motor speed is automatically controlled by the HVAC control module based on the temperature setting, but can be manually overridden.

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 mode doors direct airflow to the instrument panel registers.
• the temperature blend doors move 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 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 mode doors direct airflow to the instrument panel registers.
• 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 side window demisters and defrost duct 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 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.

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 turned on in DEFROST. The A/C compressor operates as long as the outside temperature is above approximately 0°C (32°F).
• blended air temperature is available.
• the blower motor is on and the speed is adjustable.

MyFord Touch® (if equipped) 

The MyFord Touch® feature can be used to store and recall the driver's preset 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 MyFord Touch®, refer to the Owner's Literature.