4-14. Aircraft APU air can be used to augment engine bleed air for operating the aircraft air- conditioning system. What valve(s) in the bleed-air system provide(s) air for this feature? 1. Air isolation valve 2. Engine bleed-air check valve 3. Engine bleed-air secondary pressure valve 4. Engine bleed-air pressure valves 4-15. What is the function of the control unit in the bleed-air “ leak detection system? 1. To close the bleed-air pressure regulator when an overheat condition occurs in the system only 2. To operate a warning light on the advisory panel when an overheat condition occurs in the system only 3. To close the bleed-air pressure regulator and light a warning light on the advisory panel when overheat occurs in the system 4. To provide a means for selecting a nonleaking system for backup Learning Objective: Recognize the operating principles and components of the air cycle air- conditioning system. 4-16. Air cycle air-conditioning systems are used in most naval aircraft for which of the following reasons? 1. The overall costs for installation and operation of air cycle systems are lower 2. Refrigerant systems do not function well at high altitudes 3. Refrigerant systems are more difficult to maintain 4. Air cycle systems are efficient for their weight and the space required and are relatively trouble free ITEMS 4-17 THROUGH 4-54 PERTAIN TO THE AIR-CONDITIONING SYSTEM IN THE F-18 AIRCRAFT. 4-17. What is the source of the cooling air used to cool bleed air in the primary and secondary heat exchangers? 1. RAM air/outside air flowing across the heat exchangers 2. AFU air being ejected across the heat exchangers 3. Bleed air modulated by a system pressure regulator valve ejected across the heat exchanger 4. Bleed air forced through the heat exchanger by the turbine compressor 4-18. What is the purpose of the secondary heat exchanger? 1. To cool the bleed air after it leaves the engine compressor section 2. To cool the bleed air before it is ejected into the primary heat exchanger 3. To cool the bleed air coming from the compressor end of the refrigeration turbine/ compressor 4. To increase the temperature of the bleed air before it enters the refrigeration turbine/compressor 4-19. What system component cools bleed air by the rapid expansion method? 1. Refrigeration compressor 2. Primary heat exchanger 3. Secondary heat exchanger 4. Refrigeration turbine 23