(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. DEFROST AIR knob In as required.
(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 35 minutes after
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 temp mode selector
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 N1
speed is above 65% RPM. When the bypass valve is
opened to a position approximately 30° from full open,
the refrigeration system will turn off.
(2) The CABIN TEMP INCR control 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
temperature mode selector in the MAN HEAT or MAN
COOL position, regulation of the cabin temperature is
accomplished manually with the MANUAL TEMP
(1) In the MAN HEAT mode, the automatic
system is overridden and the system is controlled by
opening or closing the two bypass valves with the
MANUAL TEMP / INCREASE / DECREASE switch.
To increase cabin temperature, hold the switch at the
INCREASE position, to decrease cabin temperature,
hold the switch in the DECREASE 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) With the cabin temperature selector
switch in the MAN COOL position, the automatic
temperature control system is bypassed. In the
manual cooling mode, the refrigeration system is on,
providing the right engine N1 speed is above 65%
RPM, however, the bypass valves may be manually
positioned for the desired temperature. Hold the
MANUAL TEMP switch in the DECREASE position
approximately one minute to fully close air-t o-air heat
exchanger bypass valves.
e. Bleed Air and Vent Control.
(1) Bleed air entering the cabin is controlled
by bleed air valve switches, placarded BLEED AIR
VALVE / OPEN / ENVIRO OFF / PNEU & ENVIRO
OFF C D T1 and ENVIRO & PNEU BLEED AIR /
PNEU ONLY / ON / BOTH T2 . When the switch is in
the OPEN / ON position, the environmental flow
control unit and the pneumatic valve are open. When
the switch is in the ENVIRO OFF or PNEU ONLY
position, the environmental flow control unit is closed
and the pneumatic bleed air valve is open; in the
PNEU & ENVIRO OFF position, both are closed. For
maximum cooling on the ground, turn the bleed air
valve switches to the ENVIRO OFF or PNEU ONLY
(2) The forward vent blower is controlled by a
switch, placarded VENT BLOWER AUTO / LOW / HI
C D T1 and VENT BLOWER AUTO / LOW / HIGH
T2 . The HI / HIGH and LOW positions regulate the
blower to two speeds of operation. In the AUTO
position, the fan will run at low speed except when the
CABIN TEMP mode selector switch is placed in the