Learjet 60 - CAB TEMP Indicator; Cooling System

Pilot's Manual
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LeaQet60
CAB TEMP INDICATOR
The CAB TEMP indicator, located on the copilot's instrument panel, is
used to provide the crew with visual indication of cabin temperature .
The indicator is calibrated from 60'F to 90'F in
three
colored segments
as follows : 60'F to 70 0 F, blue ; 70'F to 80'F, green ; 80'F to 90'F, red . The
indicator operates on
28 VDC supplied through the
1-amp CABIN
TEMP IND circuit breaker on the copilot's circuit breaker panel .
R-12 COOLING
SYSTEM (Aircraft 60-001 thru 60-173)
The R-12 vapor cycle cooling
system is installed
for cockpit and cabin
cooling during ground operations, inflight cooling, and cabin dehu-
midification . Power must be supplied by an engine generator, ground
power
unit
or APU . When the COOL-OFF switch is set to COOL, pow-
er is supplied to the compressor motor and the system refrigerant is
compressed and circulated under high pressure through a receiver/de-
hydrator
(dryer) to the cockpit and cabin evaporators . A cockpit blow-
er, located below the cockpit floor, and a cabin blower, located in the aft
cabin overhead, circulate air through the system evaporators to pro-
vide cooling . Also, pressurization bleed air is used to provide airflow
through the cabin evaporator . System overpressurization protection is
provided by a pressure switch downstream of the compressor motor .
The switch will open to break the motor power circuit should system
pressure exceed limits and reset when pressure drops to within limits .
If the cabin temperature control valve exceeds approximately 15' open
(HOT), a switch will open to disable the compressor motor to prevent
overloading the system . As soon as the valve opening returns to 15' or
lea, power will be restored . The refrigeration system is automatically
cutout during engine start, STAB WING HEAT operation, and inflight
when only one generator is operating . When the aircraft is on external
power, the compressor motor is powered by 28 VDC supplied through
a 175-amp current limiter connected to the battery charging bus and a
power contactor . When the generators are operating, the compressor
motor A
powered
by 28 VDC
supplied
through two power contactors
and two 175-amp current limners connected to the generator buses . A
fault
isolator
will
remove power from the compressor motor should a
fault occur which causes the compressor load to become unequally
shared between the generators (except during single generator opera-
tion on the ground) . System control circuits, including the cabin blow-
ers, we powered by 28 VDC supplied through the 5-amp FREON
CONTROL circuit breaker on the pilot's circuit breaker panel . The cab-
in blowers are powered by 28 VDC through a 50-amp current limiter .
Speed control circuits for the cabin blowers are powered through the
5-amp CABIN FAN circuit breaker on the copilot's circuit breaker pan-
el . The cockpit blower (including speed control circuit) is powered by
6-36
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PM-123
Change 4