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then passes out of the exchanger into the cabin air distribution ducts.
Thetemperature of the conditioned air is controlled by the hot air bypass
(H) valve. This valve bypasses some of the bleed air around the
heat exchanger and mixes it directly with the conditioned air exiting
the heat exchanger. H-valve position, thus, temperature regulation, is
controlled by the pneumatically operated temperature control system
Whenever the cabin temperature AUTO-MAN selector knob is rotated
to AUTO, the temperature controller will automatically maintain
the temperature set with the temperature selector. With the mode selector
in AUTO and the HOT-COLD temperature selector knob set to
COLD the temperature selector needle valve opens and reduces the
pressure to the cabin temperature sensor. The decreased pressure
causes the cabin temperature sensor bleed path to open and allows
the sensor to vent more of the pressure to ambient. The decreased
pressure allows the H-valve to close and routes bleed air through the
heat exchanger, then into the cabin at a lower temperature. When the
temperature selector is set to HOT the temperature selector needle
valve closes and raises the pressure to the cabin temperature sensor .
The increased pressure causes the cabin temperature sensor bleed
path to close and increases pressure to the Hvalve. The increased
pressure allows the H-valve to open and bypass more hot air into the
cabin distribution system. The cabin temperature sensor's fan blows
cabin air across the sensor, and causes the sensor to meter more or
less pressure, depending on the temperature of the cabin air and the
selected temperature. The temperature sensor fan is inoperative when
the COOL-OFF switch is set to COOL. When the mode selector is set
to MAN, the cabin temperature sensor and duct temperature sensor
are removed from the system, and the pressure to the H-valve is controlled
directly by the HOT-COLD temperature selector. Setting the
temperature selector to COLD, bleeds off a greater amount of the regulated
pressure and allows the H-valve to route more bleed air
through the heat exchanger. Setting the temperature selector to HOT
closes the bleed path and increases the pressure at the H-valve. The
valve opens and bypasses more bleed air directly into the cabin air
distribution ducts.
6- 26
PM-121
Original
Learjet 31A
Pilot's Manual
CA&N MR
DISTRIWTION
BLEED AIR
TAILCONE BLEED-AIR DISTRIBUTION
Figure 6-10
CABIN MR
OIBTIBBuno"
CONDITIONED AIR
PM-121
6-27
Original
Pilot's Manual
Learjet 31A
CAB AIR SWITCH
The CAB AIRswitch, located on the pressurization control panel, controls
the flow control valve. With the BLEED AIR switches ON, setting
the CAB AIR switch ON will de-energize the flow control valve
controlling solenoid and allow system pressure to the valve's controlling
chambers. Internal pressures will position the valve butterfly,
controlling bleed air flow to the heat exchanger. Setting the CAB AIR
switch ON also energizes the cabin temperature sensor blower. Setting
theCAB AIR switch OFF will energize the valve control solenoid
which will shutoff control pressure and allow the valve butterfly to
block bleed air flow.
AUTO-MAN SELECTOR
An AU'PO-MANmode selector, located on the copilot's switch panel,
provides for automatic or manual mode operation of the cabin temperature
control system. When in AUTO mode, the system temperature
controllers automatically position the H-valve butterfly. In the
MAN mode, the HOT-COLD selector directly regulates the H-valve
controlling pressure.
HOT-COLD TEMPERATURE SELECTOR
The HOT-COLD temperature selector is located on the copilot's
switch panel. In system AUTO mode, the temperature selector is used
to select the desired cabin temperature to be maintained automatically
by the temperature control system. In MAN mode, the temperature
selector directly varies the regulating pressure to position the Hvalve.
In AUTO mode, rotating the knob clockwise from COLD to
HOT is equivalent to selecting temperatures ranging from 60°F (16°C)
to 90OF (3200.
6- 28
PM-121
Original
Learjet 31A
Pilot's Manual
SHOULDER
OUTLET
CHECK VALVE
VARIABLE
OPENING
OUTLET
"
AUX HEATER
AIR DISTRIBUTION SCHEMATIC
(With R12 Freon Cooling System)
Figure 6-11
SHOULDER
OUTLET
PM-121
6-29
Change 4
Pilot's Manual
Learjet 31A
AIR DISTRIBUTION SCHEMATIC
(with R134ACooling System)
Figure 6-12
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