CHAPTER 21
ENVIRONMENT CONTROL
21-00 Description
Fresh air vents are located in each door and in the nose. Door vents are opened and closed
using the knob near the vent door hinge. A rotating knob is provided to seal and lock vents
closed. For maximum ventilation, open door vents wide during hover but only one inch or
less during cruise. The rotating knob can be used to hold vents partially open.
See Chapter 52 for door vent maintenance instructions.
The fresh air inlet in the nose is opened by pulling the vent handle on the console face.
Rotating the vent handle clockwise will lock its position. Air from the nose inlet is directed
along the inside surface of the windshield for defogging as well as for ventilation.
The optional cabin air conditioning system, shown schematically in Figure 21-2, is similar to
conventional automotive and light aircraft systems. The system consists of a compressor
mounted immediately aft of the main gearbox, a condenser mounted to the vertical firewall
in the engine compartment, an evaporator mounted to the front of the center seat support,
a blower, an overhead outlet duct, and interconnecting lines and hoses. The system uses
R134a refrigerant.
The compressor is belt-driven, by a pulley mounted to the main gearbox tail rotor drive yoke
assembly, and is equipped with an electromagnetic clutch. When the system is off, the
compressor clutch is disengaged, allowing the compressor pulley to freewheel.
Cooling air for the condenser is supplied via an opening in the belly. The engine cowling air
scoop collects the necessary cooling air for the condenser during forward flight. In a hover,
electric fans help to draw cooling air through the condenser.
The evaporator blower draws warm cabin air though the evaporator inlet grill and evaporator,
where the air is cooled. Cool air is drawn through the blower and blown through ducts under
the center seat, up the cabin aft wall, and to the overhead duct.
The system is controlled by a toggle switch on the overhead duct which allows selection of
off, low, and high fan settings. The compressor requires main rotor gearbox oil pressure to
engage. The compressor is automatically engaged by switching the fan on. A temperature
(freeze) switch disengages the compressor when evaporator temperature drops below
freezing. Safety (pressure) switches disengage the compressor if excessive refrigerant
leakage occurs or if refrigerant pressure is excessive. When the collective is lowered to the
full-down position another switch disengages the compressor for 10 seconds to ensure that
aircraft performance is not affected. All circuits are protected by the 25 amp A/C circuit
breaker; the evaporator blower, the condenser fans, and the compressor clutch circuits are
further protected by fuses.
Bleed air from the engine compressor is used for cabin heat. Tubing routes hot air from the
engine to outlets forward of the tail rotor pedals and in the rear footwells. A heater control
knob located to the left of the cyclic stick actuates a valve in the aft end of the control
tunnel through a push-pull cable to control cabin heat. Because the cabin heat uses engine
compressor air, some performance degradation occurs with heat ON.
CAUTION
In case of engine fire, cabin heat should be turned off.
MAY 2015 Chapter 21 Environment Control Page 21.1
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