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
