(2) If the cockpit is too hot:
1. CABIN AIR Knob As required.
2. PILOT and COPILOT AIR Knobs In
3. DEFROST AIR Knob In as required.
b. Cooling Mode.
(1) If the cockpit is too cold:
1. PILOT and COPILOT AIR Knob In
(2) If the cockpit is too hot:
1. PILOT and COPILOT AIR Knobs
Out as required.
2. CABIN AIR Knob Close in small
increments. Allow 3 - 5 minutes after
stabilize. If CABIN AIR knob is
completely closed before obtaining
satisfactory cockpit comfort, it may be
BLOWER switch in the ON position
to activate the aft evaporator and re-
circulate cabin air.
c. Automatic Mode Control. When the AUTO
mode is selected on the CABIN TEMP MODE switch,
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.
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 N1
speed is above 65%. When the bypass valve is
opened to a position approximately 30° from full open,
the refrigeration system will turn off.
The CABIN TEMP control rheostat provides
regulation of the temperature level in the automatic
mode. A temperature-sensing unit in the cabin, in
conjunction with the control setting, initiates a heat or
cool command to the temperature controller for
desired cockpit and cabin environment.
d. Manual Mode Control. With the CABIN
TEMP MODE switch in the MAN HEAT or MAN COOL
position, regulation of the cabin temperature is
accomplished manually with the MANUAL TEMP
(1) MAN HEAT Mode. In the MAN HEAT
mode, the automatic system is overridden and the
opening and closing of the two bleed air bypass valves
using the MANUAL TEMP switch controls the system.
To increase cabin temperature, hold the switch to the
INCR position; to decrease cabin temperature, hold
the switch in the DECR position. Allow approximately
30 seconds per valve to drive the bypass valves to the
fully open or fully closed position. Only one valve
moves at a time.
(2) CABIN TEMP Mode. With the CABIN
TEMP MODE switch in the MAN COOL position, the
automatic temperature control system is bypassed.
When the left bypass valve reaches a fully closed
position, the refrigeration system will begin cooling,
provided the right engine N1 speed is above 65%.
When the bypass valve is opened to a position
approximately 30° from full open, the refrigeration
system will turn off. Hold the MANUAL TEMP switch
to DECR position for approximately one minute to fully
close air-to-air heat exchanger bypass valves.
(3) Two switches, placarded
RIGHT BLEED AIR VALVES OPEN / ENVIR OFF /
INSTR & ENVIR OFF, control the bleed air entering
the cabin. When a switch is in the OPEN position, the
environmental flow control unit shutoff valve and the
pneumatic shutoff valve are open. When the switch is
in the ENVIR OFF position, the environmental flow
control unit shutoff valve is closed and the pneumatic
bleed air valve is open. In the INSTR & ENVIR OFF
position, both are closed. For maximum cooling on the
ground, place the bleed air valve switches in the
ENVIR OFF position.
(4) Forward Vent Blower. The forward vent
blower is controlled by a switch placarded VENT
BLOWER HIGH / LO / AUTO. The HIGH and LO
positions regulate the blower in two speeds of
operation. In the AUTO position, the fan will run at low
speed except when the CABIN TEMP MODE switch is
placed in the OFF position. In the OFF position, the
blower will not operate.