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FANswitch clockwise out of the off detent position will activate the aft
cockpit fan and vary the speed ofboth the forward and aft cockpit fans.
To provide supplemental air circulation, the CREW FAN switch is rotated
clockwise out of the off detent position until the desired fan speed
is attained . The aft fan will force air through the cockpit and cabin overhead
distribution ducts to provide cooling or circulate air when the air
circulation mode is selected. Air circulated by the aft cockpit fan is exhausted
through the cockpit and cabin overhead eyeball outlets when
they are rotated to the open position. Air circulated by the forward
cockpit fan isexhausted through two louvered outlets in the cabinet behind
the copilot's seat.
R1 34A COOLING SYSTEM
The refrigerant-type (R134A) cooling system is installed for cockpit and
cabin cooling during ground operations, inflight cooling, and cabin dehumidification.
On the ground, power must be supplied by either aircraft
electrical system generator providing 28 VDC, or ground power
unit. In flight, the airconditioning system must beoperated byboth aircraft
generators on line. When the COOL-OFF switch is set to COOL,
power is supplied to the R134A compressor motor and the system refrigerant
is compressed and circulated under high pressure through a
receiver/dehydrator (dryer) to the system forward and aft evaporators.
The Toward evaporator/blower unit is located above the cockpit headliner.
It provides airflow for the cockpit, as well as windshield defog.
Cabin air is drawn into the evaporator coil and the fan then delivers the
conditioned air to individual gaspers and an "eyebrow" outlet duct.
The evaporator blower can be operated in the "FAN" position to recirculate
cockpit air without cooling.
The cabin evaporator/blower unit is located in the aft section of the
cabin ceiling. It contains an evaporator, two separate blowers and two
heating elements that provide auxiliary heating. The first blower provides
cooling airflow to the cabin gaspers and the second blower provides
flood duct cooling to the aft cabin. This blower is also used in the
auxiliary heat mode. The evaporator blowers can be operated in the
"FAN" position to recirculate cabin air without cooling.
Refrigerant system is protected against overpressure conditions by two
separate safety devices. The first is a binary high/low pressure switch
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Pilot's Manual
Learjet 31A
located on the compressor discharge port. This switch will open at approximately
350 psig and will interrupt power to the compressor control
circuit. This in turn will de-energize the compressor motor relay
and remove power to the compressor motor. The refrigerant system
pressure will then drop. The switch will also interrupt power to the
compressor control circuit under low pressure conditions. This low
pressure switch mayalso shut down the compressor if the average refrigerant
temperature between the cabin and tailcone is 35°F (1 .7°C) or
less. The second overpressure safety device is a fuse plug located on the
receiver/dryer bottle . This plug will vent the system refrigerant safely
overboard in the event of a system pressure in excess of 425 psig. The
refrigerant system is automatically cutout during engine start. System
safety features also include electrical interlocking and load shedding.
In flight, the air conditioning system can be operated from the aircraft
electrical system only with both generators oat-line. Loss of either generator
will automatically shed the air conditioning system electrical
loads, except for the minimal loads of the evaporator fans. The compressor
drive/condensor fan motor is powered by 28 VDC supplied
through a 175-amp current limiter. System control circuits are powered
by 28 VDC supplied through the 7.5-amp COOL-CREW FAN circuit
breaker on the pilot's circuit breaker panel. The gasper fan, located in
the aft evaporator, is powered by 28 VDC supplied through the 15-amp
GASPER FAN circuit breaker on the co-pilot's circuit breaker panel.
The cockpit fan, located in the forward evaporator and blower unit, is
powered by 28 VDC supplied through the 7.5-amp COOL-CREWFAN
circuit breaker on the pilot's circuit breaker panel. The flood fan, located
in the aft evaporator, is powered by 28 VDCsupplied through a 15-
amp FLOODFANcircuit breaker on the pilot's circuit breaker panel.
COOLOFF SWITCH
TheCOOL-OFF switch, located on the copilot's switch parkel, controls
the R134A cooling system. Whenset to COOL, the switch allows power
to the compressor motor, flood fan, gasper fan and crew fan circuits.
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