TM 55-1510-219-10
limits. When the low or high pressure switches are
activated, a reset switch/light assembly located in the
nosewheel
well
is
activated
to
prevent
further
compressor operation.
(4)
Thermal sense switch. A 33° thermal
sense switch is installed on the forward evaporator.
This sense switch actuates a hot gas bypass valve
which bleeds off a portion of the refrigerant from the
forward evaporator, thereby preventing icing of the
evaporator.
(5)
Condenser blower. A vane-axial blower
draws air through the condenser on the ground as well
as in flight. The current limiter for this blower is located
on the DC distribution panel in the lower equipment bay.
When the cabin temperature mode selector switch is set
to the A/C COLD OPN position, the condenser blower
will be off, and will remain off until the added high
pressure
switch
senses
a
compressor
discharge
pressure equal to the pressure it is set to. The
condenser blower will then remain in operation until the
low pressure switch senses that the system pressure has
dropped to the pressure it is set to.
(6)
Air conditioning cold start bypass valve.
Low
ambient
temperature
operation
of
the
air
conditioning system is accomplished by means of a
bypass valve located in the nose wheel well, an
additional high pressure switch, and an additional low
pressure switch, both of which are located in the right
inboard wing leading edge. The cold start bypass valve
opens when the cabin temperature mode selector switch
is set to the A/C COLD OPN position to enhance
refrigerant flow at low temperatures and improve air
conditioner performance.
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
ENVIRO OFF position.
2.
Cabin temperature mode selector
switch MAN COOL.
(3)
Air conditioning cold start 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 conditioner system
to exceed the compressor low
pressure
limit
switch
setting,
illuminating the reset switch in
the
nosewheel
well,
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.
2-69. 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 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.
2-70. ENVIRONMENTAL CONTROLS.
An environmental control section on the overhead
control panel (fig. 2-18) provides for automatic or
manual control of the system. This section contains all
the major controls of the environmental function
including bleed air valve switches, a vent blower control
switch, an aft vent blower switch, a manual temperature
switch for control of the heat exchanger valves, a cabin
temperature level control,
2-56
