Learjet 60 - Air Conditioning and Heating; Primary Heating and Cooling-Bleed Air

Learjet
60

Pilot's Manual
AIR CONDITIONING AND HEATING
Primary heating and cooling is accomplished by controlling the tem-
perature of the bleed air entering the independently controlled cockpit
and
cabin air distribution systems . On aircraft 60-001 thru 60-173, an
R-12 vapor
cycle
cooling
system is installed to provide additional cool-
ing at lower altitudes and during ground operations . On aircraft 60-174
and subsequent, an R-134A vapor cycle cooling system is installed to
provide additional cooling . An auxiliary (electrical) heating system is
installed to provide additional heating for the cabin, if desired .
PRIMARYHEATING AND COOLING-BLEED AIR
Cockpit and cabin temperature is regulated by controlling the temper-
ature
of
the pressurization bleed air entering
the
cockpit and cabin air
distribution systems . With the BLEED AIR switches ON and the CAB
AIR switch ON, engine bleed air is admitted to the ram air heat ex-
changer through a flow
control
valve
. The bleed air is cooled in the heat
exchanger by ram air entering the dorsal inlet, passing through the ex-
changer, and then exiting overboard . The conditioned bleed air then
passes out of the exchanger into the cockpit and cabin air distribution
ducts .
The
temperature of the conditioned air is controlled by the tem-
perature control valve
on
each
distribution system duct . These
valves
bypass some of the bleed air around the heat exchanger and mix it di-
rectly with the conditioned air exiting the heat exchanger .
Temperature
control valve position, thus, temperature regulation, is
pneumatically controlled by the electrically
operated
temperature
con-
trol system . Whenever either cabin or cockpit temperature AUTO-
MAN switch is set to AUTO, the respective system temperature con-
troller will automatically maintain the temperature set with the (CREW
or CABIN) COLD-HOT
selector
. The
cabin temperature AUTO-MAN
switch also has a CABIN position which allows the temperature to be
set using a temperature' control panel in the cabin area . The controllers
maintain the selected temperature by comparing input signals from
various
temperature sensors and then electrically controlling the
torque motors that provide pneumatic pressure (servo air) to the tem-
perature control valves . Duct temperature sensors are installed in each
system to close the temperature control valves and light the DUCTOV
HT
caution
light
whenever excessively high duct temperatures are
sensed . The cockpit and cabin air temperature sensors have small blow-
ers that draw air past the sensing elements to assure rapid sensing of
temperature changes .
PM-123
Change 4
6- 31