CHAPTER 4 AIR-CONDITIONING SYSTEMS

CHAPTER 4 AIR-CONDITIONING SYSTEMS AMEs Chapter Objective: Upon completion of this chapter, you will have a working knowledge of the operating principles and components of air-condi- tioning. maintain the air-conditioning and pressurization systems of naval aircraft. These systems provide heating and cooling of the cabin and, at altitude, the pressurization required for breathing. As an AME, you will be assisting aircrews and troubleshooting discrepancies. A good knowledge of the systems is necessary to perform effectively. This chapter uses the S-3 environmental control system as the basis for discussion. To simplify matters, we have divided the system into two subsystems: bleed air and air-conditioning. BLEED-AIR SYSTEM Learning Objective: Identify the operating principles and components of a bleed-air system. The bleed-air system is the air source for the environmental control system (ECS) and for deicing functions. There are three sources of bleed air available. The primary source is the com- pressor sections of the two aircraft engines. Secondary sources are from the auxiliary power unit (APU) and from an external air supply such as support equipment (SE). SYSTEM OPERATION As previously stated, the source of air for the bleed-air system may be from the aircraft engines, the APU, or SE. Operation of the system using each of these sources is presented in the following paragraphs. Frequent referral to the bleed-air system schematic (fig. 4-1) will aid you in under- standing the material. Engine Bleed Air The engine bleed air is extracted from the 10th- and 14th-compression stages of each engine. The low-stage bleed-air check valve supplies the 10th- stage air, which is the primary source for operation of the ECS. When 10th-stage air is insufficient to meet ECS demands, 14th-stage air is supplied through the high-stage, bleed-air regulator valve. One bleed-air shutoff valve is installed in each engine pylon downstream of the 10th- and 14th- stage engine-compressor bleed ports. The bleed- air shutoff valves are controlled by switches on the eyebrow panel in the flight station. Lights on the instrument panel indicate the position of the bleed-air shutoff valves. The lights illuminate when the valves are closed regardless of the position of the switches. When open, the bleed-air shutoff valves allow engine compressor bleed air to flow into the bleed-air manifolds. The bleed-air manifold distributes bleed air from both engines into the air-conditioning and pressurization systems. Two crossover duct isolation check valves prevent the possibility of an overbleed of both engines should a rupture occur in the left or right bleed-air manifold. The check valves, located in the left and right manifolds, allow bleed air to flow in one direction 4-1