The Refrigerant Cycle

For information regarding base refrigerant operation within the HVAC system, refer to the current Ford Web Based Technical Training courses. The diagram below shows the refrigerant system state in each component on this vehicle.

The following statements apply to this refrigerant 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 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.

TXV Type Refrigerant System State and Flow - GTDI 

Courtesy of FORD MOTOR COMPANY

TXV Type Refrigerant System State and Flow - Ti-VCT 

Courtesy of FORD MOTOR COMPANY

Compressor Anti-Slugging Strategy (CASS) 

Liquid refrigerant may accumulate in the A/C compressor under certain conditions. To reduce damage to the A/C compressor, Compressor Anti-Slugging Strategy (CASS) is utilized.

CASS is initiated only under specific conditions:

• Ignition is off for more than 8 hours
• Ambient temperature is above -4 °C (25 °F)
• Battery voltage is above 8.5 volts during engine cranking

When these conditions are present, the PCM activates the A/C control relay prior to cranking of the engine. The A/C control relay engages the A/C compressor for approximately 4-15 A/C compressor revolutions or a maximum of 2 seconds (depending upon vehicle application), allowing the liquid refrigerant to be pushed from the A/C compressor. CASS is initiated by the PCM regardless of the HVAC system settings.