Specifications

SECTION II
AIRPLANE AND SYSTEMS
MODEL 560
AIR CONDITIONING
Air conditioning for the cabin is provided by routing engine bleed air through precoolers and in turn
through the air cycle machine which conditions the air prior to distribution to the cabin. Cabin overhead and
underfloor ducting is used to distribute the conditioned air. A standard R134A vapor cycle air conditioning
system is also available for additional cooling up to 18,000 feet.
The air cycle machine located in the tailcone compartment, cools engine bleed air to approximately
2°C (35°F). Bleed air enters the air cycle machine through two bleed air shutoff and pressure regulating
valves (LH, RH) and passes over a primary heat exchanger. The air is then compressed by a
turbine-driven compressor and passed over a second heat exchanger. Finally, the air drives a turbine which
extracts energy and cools the air further. Expansion provides the final cooling. The advantages of the
compression cycle are twofold: (1) the compressor section provides a load for the turbine to work against
and (2) compressing and heating the air increases the efficiency of the second heat exchanger. Fresh air
enters the tailcone through the flush scoops in the dorsal fin. A small fan, driven by the air cycle machine,
pulls the fresh air over both heat exchangers and the precooler and dumps it overboard through a vent in
the tailcone.
Figure 2-25. Pressurization - Environmental Control Panel (Typical)
To warm the cabin to a desirable temperature, a bypass valve allows some hot engine bleed air to
bypass the ACM and mix with the cold air exhausted from the air cycle machine. The bypass valve is
controlled by the automatic or manual temperature control located on the pressurization environmental
control panel. With the temperature control selector in the MANUAL position, the bypass valve can be
controlled manually by the MANUAL HOT/MANUAL COLD switch. The switch has three positions, spring-
loaded to the center (OFF) position. When the switch is deflected toward the MANUAL HOT position, the
bypass valve is driven open, allowing more hot bleed air to bypass the ACM and mix with the cold air
exhausted from the air cycle machine. When the switch is released, the bypass valve will remain at that
position. When the switch is moved toward the MANUAL COLD position, the bypass valve is driven closed.
The bypass valve, when manually controlled, will travel from full open to full closed in approximately ten
seconds. When AUTOMATIC temperature control is selected, the cabin temperature will be automatically
controlled, corresponding to the position of the automatic temperature selector. Response rate in automatic
depends on temperature conditions. Two air duct temperature sensors are linked to the automatic
temperature control selector to drive the bypass valve towards the desired position. Should the duct
temperature become excessively hot, the amber AIR DUCT O'HEAT annunciator panel light will illuminate.
This is an advisory light and corrective action, lowering the cabin temperature, should be accomplished to
prevent system damage.
I 2-54 Configuration AA 56OMB-01