TM 55-1510-222-10
draws air through the condenser when aircraft is on the
ground. The blower is protected by a 50 ampere circuit
breaker located beneath the aisleway. When the cabin
temperature mode selector switch is set to the AC
COLD OPN position during ground operation, the
condenser blower will be off initially, and will remain off
until compressor discharge pressure equals the pressure
setting of the blower control high pressure switch. The
blower will remain in operation until system pressure
drops to equal the setting of the blower control low
pressure switch.
(6)
Air conditioning cold operation
bypass valve. Selecting the A/C COLD OPN mode on
the cabin temperature mode selector switch permits the
operation of the air conditioning system by overriding
the refrigerant low pressure switch. This allows the air
conditioning system to operate in the manual mode.
Starting the compressor in this optional mode at low
ambient temperature will decrease the operational life of
the compressor by five hours each time the air
conditioning system is started below 10° C using this
mode (AC COLD OPN). If the air conditioning system
has been operating in the normal mode during flight,
and due to decreasing ambient temperatures make it
necessary to switch to the AC cold operation mode,
there will be no degradation in the mean time between
failure for the compressor.
(7)
Air conditioner cold operation.
Cold air conditioner operation mode is provided to allow
the air conditioner to operate in the event of a hot cabin
and an outside air temperature of less than 10° C. At an
OAT of less than 10° C, a green advisory annunciator
placarded
AC
COLD
OPN,
located
on
the
caution/advisory annunciator panel (fig. 2-5), will
illuminate. This advises the crew that if air conditioning
is required, the cabin temperature mode switch must be
in the A/C COLD OPN position. This causes the air
conditioner compressor to run continuously and the
temperature controller to operate the bypass valve.
b. Normal Operation.
(1)
Automatic cooling mode.
1.
Bleed air valve switches - OPEN, LEFT
and RIGHT.
2.
Cabin temperature mode selector switch
- AUTO.
3.
Cabin temperature control rheostat - As
required.
4.
Cabin, cockpit and defrost air knobs -
As required.
(2)
Manual cooling mode.
1.
Bleed air valve switches - OPEN, LEFT
and RIGHT.
NOTE
For maximum cooling on the ground,
set the bleed air valve switches to the
PNEU ONLY position.
2.
Cabin temperature mode selector switch
- MAN COOL.
(3)
Air conditioning cold operation
mode. (Used if ambient temperature is between 10° C
and -25° C).
NOTE
Setting the cabin temperature mode
selector switch to the A/C COLD OPN
position
at
ambient
temperatures
below -25 ° C may cause the air
conditioning system to exceed the
compressor low pressure limit switch
setting,
terminating
compressor
operation, and thereby rendering the
system inoperative for the remainder
of the flight.
1.
Bleed air valve switches - OPEN, LEFT
and RIGHT.
2.
Cabin temperature mode selector switch
- A/C COLD OPN.
3.
Cabin temperature control rheostat - As
required.
4.
Cabin, cockpit and defrost air knobs -
As required.
2-70.
UNPRESSURIZED VENTILATION.
Ventilation is provided by two sources. One source is
through the bleed air heating system in both the
pressurized and unpressurized mode. The second
source of ventilation is obtained from ram air through
the condenser section in the nose through a check valve
in the vent blower plenum. Ventilation from this source
is in the unpressurized mode only with the CABIN
PRESS DUMP switch in the DUMP position. The check
valve closes during pressurized operation. Ram air
ventilation is distributed through the main ducting
system to all outlets. Ventilation air, ducted to each
individual eyeball cold air outlet, can be directionally
controlled by moving the ball in the socket. Volume is
regulated by twisting the outlet to open or close the
valve.
2-71.
ENVIRONMENTAL CONTROLS.
An environmental control section on the overhead
2-60
