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.

Servicing Equipment preferably together as a system, with refrigerant and/ or lubricating oil. Servicing of the vapor cycle system involves The vapor cycle charging cart (fig. 3-18) is evacuating and charging the condenser and used to replenish the vapor cycle refrigeration evaporator group assemblies either separately or system with refrigerant and the compressor with

Figure 3-18.- Vapor cycle charging cart.

lubricating oil. The major components of the cart are labeled in figure 3-18. The Freon storage bottle has a capacity of 25 pounds of Freon. The bottle is restrained in the cart by quick-release restraining straps, which permit rapid removal and replacement of depleted bottles. The electric motor-driven vacuum pump is used to evacuate a refrigerant system prior to recharging it with Freon. Evacuating or pulling a vacuum on the system for a short period of time causes any moisture in the system to be vaporized and withdrawn from the system. Moisture in the system, if of sufficient quantity, can freeze at the expansion valve, thus allowing no Freon into the evaporator and cooling would stop. The vacuum pump has a displacement of 3 cubic feet per minute (cfm) and is rated for continuous duty. The heater tank has a capacity of 360 cubic inches and an operating pressure rating of 200 psi at 125 F (52 C). A liquid level sight gauge, mounted vertically on the heater tank, indicates the level of liquid Freon in the tank. A scale, graduated in pounds and ounces, is mounted alongside the sight gauge and ranges from 0 to 17 pounds. The tank is also equipped with a compound pressure gauge, which is graduated from 0 to 30 inches Hg (mercury vacuum) and 0 to 300 psi pressure. A heating blanket surrounds the heater tank and is used to heat the refrigerant for building up tank pressure sufficient for charging a system. The oil charging cylinder stores Ansul 150 lubricating oil used to replenish the vapor cycle compressor oil supply. The cylinder has a capacity of 68 cubic inches and an operating pressure of 100 psi at 125 F. The cylinder is equipped with an oil level sight gauge and an oil charging pressure gauge. A scale, graduated in centimeters, is mounted beside the sight gauge and ranges from 0 to 800 cc. The flexible evacuation and charging hoses are both 180 inches long to accommodate hooking the cart to the unit being evacuated or charged without removing the unit from the aircraft. An aircraft power cable connects primary electrical power from the cart to the aircraft. A deck edge power cable or power cable from electric generating equipment provides power to the cart. 

Safety Precautions 

To prevent injury to personnel and damage to equipment, you must observe the following safety precautions and handling procedures when working with Freon gas: 

1. Protective equipment (apron, gloves, goggles, and face mask) must be worn. 

2. If liquid Freon comes in contact with the skin, treat the skin for frostbite. 

3. If liquid Freon comes in contact with the eyes, medical attention must be sought immediately. The following first aid treatment should be administered: Do not rub or irritate the eyes; drop sterile mineral oil into the eyes; then wash the eyes with a boric acid solution if the irritation continues. 

4. Freon is stored in cylinders that are color-coded orange with appropriate lettering for identification. These cylinders should be handled carefully because the pressure inside the cylinder depends upon the ambient temperature. Refrig-erant cylinders should not be exposed to high temperatures or flames. Cylinders that are used for high-pressure liquids should never be thrown around, dropped, or used for anything other than their intended purpose. Refrigerant cylinders should never be filled to more than 85 percent of their capacity. 

5. Freon tends to dissolve natural rubber; therefore, only the recommended gaskets, O-rings, and packings should be used in the vapor cycle system.