TM 1-1510-262-10
(b) Cabin temperature mode selector switch -- A/C COLD OPN.
(c) Cabin temperature control rheostat -- As required.
(d) Cabin, cockpit and defrost air knobs -- As required.
2-74. 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.
2-75. ENVIRONMENTAL CONTROLS.
An environmental control section on the overhead control panel (Fig. 2-13) 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, forward and aft vent blower switches, manual temperature switch for control of the heat exchanger valves,
a cabin temperature level control, and the cabin temperature mode selector switch for selecting automatic heat-
ing/cooling or manual heating/cooling.
a. Heating Mode.
(1)
If the cockpit is too cold:
PILOT and COPILOT AIR knobs -- As required.
(a)
DEFROST AIR knob -- As required.
(b)
CABIN AIR knob -- Pull out in small increments. Allow 3-5 minutes after each adjustment for system
(c)
to stabilize.
(2)
If the cockpit is too hot:
CABIN AIR knob -- As required.
(a)
PILOT and COPILOT AIR knobs -- In as required.
(b)
DEFROST AIR knob -- In as required.
(c)
b. Cooling Mode.
(1)
If the cockpit is too cold:
PILOT and COPILOT AIR knob -- In as required.
(a)
DEFROST AIR knob -- In as required.
(b)
(c)
Overhead cockpit outlets -- As required.
(2) If the cockpit is too hot:
(a) PILOT and COPILOT AIR knobs -- Out as required.
(b) CABIN AIR knob. -- Close in small increments. Allow 3 - 5 minutes after each adjustment for system
to stabilize. If CABIN AIR knob is completely closed before obtaining satisfactory cockpit comfort, it
may be necessary to place the aft vent blower switch in the ON position to activate the aft evaporator to
re-circulate cabin air.
c. Automatic Mode Control. When the AUTO mode is selected on the CABIN AIR MODE SELECT switch, the
heating and air conditioning systems are automatically controlled. When the temperature of the cabin has reached
the selected setting, the automatic temperature control allows heated air to bypass the air-to-air exchangers in the
wing center section. The warm bleed air is mixed with the cooled air. The rear evaporator picks up re-circulated
cabin air only.
(1) When the automatic control drives the environmental system from a heat mode to a cooling mode,
the bypass valves close. When the left bypass valve reaches a fully closed position, the refrigeration system will
begin cooling, provided the right engine N 1 speed is above 65%. When the bypass valve is opened to a position
approximately 30 from full open, the refrigeration system will turn off.
2-69
