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ducts to provide cooling or circulate air when the air circulation mode
is selected. Air circulated by the cockpit fan is exhausted through the
cockpit and cabin overhead eyeball outlets when theyare rotated to the
open position.
Learjet 31A
Pilot's Manual
R12 FREON COOLING SYSTEM (Aircraft With Forward Evaporator
and Blower Unit)
The refrigerant-type (freon) cooling system is installed for cockpit and
cabin cooling during ground operations, inflight cooling below 35,000
feet, and cabin dehumidification. Power must be supplied by an engine
generator or ground power unit. When the COOL-OFF switch is set to
COOL, power is supplied to the freon 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.A cockpit fan and cabin blower, located in the aft evaporator
and blower unit, circulate air through the system aft evaporator
to provide cooling.Aseparate cockpit fan, located in the forward evaporator
and blower unit, circulates air through the system forward evaporator
to provide cooling. Freon system overpressurization protection
is provided by a pressure switch downstream of the compressor. The
high pressure switch will open tobreak themotor power circuit should
system pressure exceed limits and reset when pressure drops to within
limits. On aum* modified per ECR 3658, "Forward Air Conditioner Improvement",
the lowpressureswitch will open tobreak the motor power
circuit should system pressurebe discharged or if atmospheric temperature
is too low. If there is a partialrefrigerant loss, the crew will notice
ajump in amperage when the system cycles an and off. The refrigeration
system is automatically cutout during engine start. The compressor
motor is powered by 28 VDCsupplied through a 150-amp current
limiter. System control circuits are powered by 28 VDC supplied
through the 7.5-amp FREONcircuit breaker on the pilot's circuit breaker
panel. The cockpit fan and cabinblower, located inthe aftevaporator
and blower unit,are powered by 28 VDCsupplied through the 15-amp
CREW ds CABFANcircuit breaker on the 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 CREW BLOWER
circuit breaker on the CABIN PWRBUS.
COOL-OFF SWITCH
The COOL-OFF switch, located on the copilot's switch panel, controls
the freon cooling system. When set to COOL, the switch allows power
to the freon compressor motor, cabin blower and cockpit fan (forward
evaporator and blower unit) circuits.
CABIN FAN SWITCH
TheCABIN FAN switch, located on the copilot's switch panel is used
to control the cabin blower and diverter doors in the aftevaporator and
blower duct housing. When the COOL-OFF switch is set to COOL and
PM-In
6-35
Change 4
Pilot's Manual
Learjet 31A
the CABIN FAN switch is in the off detent, the cabin blower will operate
on high speed. Rotating the CABIN FAN switch clockwise out of the
off detent position will vary the speed of the cabin blower. To provide
supplemental air circulation, the COOL-OFF switch is set to OFF and
the CABIN FAN switch is rotated clockwise out of the off detent position
until the desired fan speed is attained . Cabin fan speed is not variable
when the auxiliary cabin heat system is operating.
CABIN BLOWER DIVERTER CONTROL
Airflow from the cabin blowers is controlled by the position of the
COOL-OFF and CABIN FAN switches . When the COOL-OFF switch is
set to the COOL position and the CABIN FAN switch is in the off detent,
the diverter doors in the evaporator duct will close and airflow
from the cabin blowers willbe diverted into the area above the interior
headliner. When the CABIN FAN switch is rotated clockwise out ofthe
off detent position, the diverter doors will open and airflow from the
cabin blowers will be directed forward. Whenever the COOL-OFF
switch is set to the OFF position, the diverter doors will remain open.
21)-173C-1
*Aftnmdifrdper ECR3658, freonlow
pressure switch is added and pressure
regulatoris deleted.
R12 FREON COOLING SYSTEM -OPTIONAL FORWARD
EVAPORATOR
Figure 6-15
6-36
PM-121
Change 4
Learjet 31A
Pilot's Manual
CREW FAN SWITCH
The CREW FAN switch, located on the copilot's switch panel, is used
to control the cockpit fans in both the forward and aft evaporator and
blower units. When the COOL-OFF switch is set to COOL and the
CREW FANswitch is in the off detent, the cockpit fan (forward evaporator
and blower unit) will operate on low speed. Rotating the CREW
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