cooled and the transfer of this heat to the primary coolant through the evaporator assembly. A header assembly attached to the discharge side of the evaporator assembly directs the secondary coolant air to distribution ducts throughout the electronic equipment compart- ment. A filter between the header assembly and the evaporator assembly removes dirt and dust particles and traps moisture from the air. The closed system consists of the evaporator group assembly and the condenser group assembly. The coolant circulates between the evaporator group assembly (where it absorbs heat) and the condenser group assembly where it discharges or dissipates the heat to the atmosphere through the vapor cycle scoop. During flight, ram air flowing through the scoop cools the condenser group assembly. The airflow through the scoop is controlled by a condenser pressure control system. The actuator in the scoop modulates the airflow through the scoop to provide sufficient cooling for con- densation of the refrigerant. When the aircraft is on the ground with engines running and ram airflow is insufficient for cooling, a condenser ejector air shutoff valve opens to permit engine bleed air to discharge through the ejector assembly. The ejector consists of a set of tubes that permit bleed air to escape into the ram air duct behind the condenser. The escaping bleed air creates a negative pressure (suction) area behind the condenser and causes ambient air to be drawn into the scoop and across the condenser. If the heat load applied to the evaporator and the ram air temperature and flow were constant, a simple opening would be all that was required to control the boiling point of the refrigerant entering the evaporator. Since these three factors are not constant, they must be compensated for. In the model VEA6-1 system, if the heat load is changed, the flow of refrigerant is changed by using a thermostatic expansion valve in place of a fixed opening. The pressure of the refrigerant in the evaporator is maintained constant, regardless of the refrigerant flow, by varying the speed of the compressor. When the EQUIPMENT COOLING switch is set to ON, solenoid-operated shutoff valves are energized and hydraulic pressure is directed to the evaporator fan motor and the compressor motor. The compressor motor will be automatically shut off when either aircraft engine is in autofeather and the landing gear is down. The evaporator fan motor will continue to operate. With the evaporator fan and compressor motors operating, low-pressure, low-temperature refrigerant Freon 12 vapor enters the compressor assembly through the low-pressure line leading from the evaporator assembly outlet. The vapor entering the compressor inlet combines with lubricating oil that is fed to the compressor. The oil-refrigerant mixture is compressed to raise its condensing temperature. From the compressor, the high-temperature, high-pressure mixture flows to the oil separator, where the oil is removed from the refrigerant vapor, filtered, and fed back to the compressor. If the refrigerant vapor pressure exceeds 250 ± 5 psi in the line downstream from the oil separator, the high-pressure cutoff switch will cause the cockpit EQUIP COOLING caution light to illuminate and the compressor motor solenoid valve to shut off hydraulic pressure to the compressor motor, thus shutting down the compressor. If the cutout switch failed to operate properly, the relief valve in the compressor discharge line would relieve the system of pressure in excess of 325 psi. Refrigerant vapor from the oil separator next enters the condenser assembly where ram air lowers its temperature and changes the vapor to a liquid. Refrigerant pressure on the high side of the system is controlled by regulating the amount of cooling air flowing across the condenser. A pressure transducer in the high side refrigerant line provides a signal to a control amplifier, which, in turn, causes the control actuator and flap to open and close as necessary to regulate pressure. The system is calibrated so that the condenser flap is fully closed when high side pressure is 107± 3 psi; fully opened at 151 ± 3 psi condensing pressure; and modulates the flap travel for intermediate pressures within that range. If the cooling air is inadequate to maintain the pressure at 151 ± 3 psi with the flap fully open, the system pressure will exceed the control range. When the pressure reaches 250 ± 5 psi, the high- -pressure cutout switch will shut down the vapor cycle system. From the condenser assembly, liquid Freon flows to the receiver in the evaporator group assembly. The receiver stores surplus refrigerant and thereby prevents surges in the refrigerant flow rate. Liquid refrigerant flowing from the receiver passes through a subcooler and then through a filter drier, where foreign matter and water are removed. Before entering the thermostatic expansion valve, the liquid refrigerant passes through a sight glass, which provides a visual 3-20