clean oil supply for compressor lubrication. The filter has a replaceable cellulose fiber element. If the filter becomes clogged, a bypass device permits unfiltered oil to circulate through the compressor when the differential pressure across the filter is greater than 18 to 22 psi. When the differential pressure across the filter is greater than 13.5 to 16.5 psi, the red indicator at the top of the filter will pop up and remain extended to provide an indication that the filter requires replacement prior to becoming completely clogged, and consequently passing contaminant oil to the compressor. The oil filter is designed with an automatic shutoff feature, which permits removal of the filter element and bowl without loss of the refrigerant charge. CONDENSER EJECTOR AIR SHUTOFF VALVE.— The purpose of the condenser ejector air shutoff valve is to increase airflow across the condenser during ground operation by discharging engine bleed air through the ejector assembly. The valve is pneumatically operated. It is controlled by a piston through a mechanical linkage and is spring loaded to the CLOSED position. A solenoid valve on the actuator chamber side of the piston acts as a bleed off for the air being fed from an upstream tap of the valve housing. This air is fed through the-hollow piston actuator shaft to the top side of the piston where it is bled off as long as the solenoid is de-energized. Energizing the solenoid closes off the actuator chamber bleed, and pressure builds up. This force overcomes spring tension and the valve opens. Any loss of pneumatic or electrical power to the valve will cause it to assume a closed position. CHARGING VALVES.— There are four backseating charging valves in the vapor cycle system—three in the evaporator group, and one in the condenser group. The valves are used to facilitate servicing of the system as one complete unit or servicing of the evaporator group or condenser group as individual units. The condenser and evaporator group assemblies are equipped with quick-disconnect refrigerant lines to allow their removal from the aircraft without a loss of refrigerant. PURGE VALVES.— The refrigerant system is equipped with two purge valves—one at the evaporator group assembly high point and the other on the condenser in the top scoop of the aircraft. The valves are similar to the charge valves. They are used to bleed the system, when required, and for attaching test equipment or the vacuum pump for system evacuation. 3-26 Maintenance Maintenance of the vapor cycle ACS, like the air cycle system, will generally require the joint efforts of personnel from the AME and the AE ratings. Malfunctions of the hydraulic motors that drive the compressor and evaporator fan will require the services of an AMH. Operational checkout of the vapor cycle system can be done in several ways. The AE can perform an operational check of the electrical portion of the system using a Cooling System Test Set, AN/ASM 232 (XN-1), with the engines not running. Performing an operational check of the complete vapor cycle system without the engines running requires external hydraulic and electrical power and a source of cool air. The cooled air is ducted into the condenser scoop inlet to provide flow through the condenser for con- densing the Freon. As was stated earlier, this function is normally done by ram air when sufficient ram airflow is available or by engine bleed air leaving the ejector nozzles and creating a pressure differential that causes sufficient flow for cooling on the ground when the engines are running. The operational check steps as specified in the applicable MIM should be performed in sequence. If a trouble occurs during a step, it must be corrected before proceeding. Isolation of the trouble can almost always be enhanced by referring to the step of the troubleshooting table that corresponds with the step of the operational checkout where the trouble occurred. Additional organizational-level maintenance on the vapor cycle system includes servicing (adding refrigerant and lubricating oil), leakage testing and correcting of leaks, and removal and installation of components. Intermediate-level maintenance of the evaporator assembly, the cindenser group assembly, and the air ejector shutoff valve is restricted to replacement of parts listed in the Spares and Repair Parts Data List provided in the intermediate repair section of the applicable MIM (Part IV). Special test equipment is required to bench test most of the vapor cycle components or assemblies; therefore, not all intermediate-level activities possess the capability to accomplish such maintenance. Since proper servicing of the vapor cycle system is one of the most important factors affecting operation, equipment used for servicing and servicing procedures are given brief coverage in the following paragraphs.