ground, turn the bleed air valve switches to the ENVIRO
The forward vent blower is controlled by a
switch placarded VENT BLOWER AUTO LOW HI. The
HI 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 OFF position. In the OFF
position, the blower will not operate.
The aft vent blower is controlled by a
switch placarded AFT VENT BLOWER OFF AUTO ON.
In the OFF position, the blower will not operate.
Section IX. ELECTRICAL POWER SUPPLY AND DISTRIBUTION SYSTEM
The aircraft employs both direct current (DC) and
alternating current (AC) electrical power. The DC
electrical supply is the basic power system energizing
most aircraft circuits. Electrical power is used to start
the engines, to power the landing gear and flap motors,
and to operate the standby fuel pumps, ventilation
blower, lights and electronic equipment. AC power is
obtained from DC power through inverters. The three
sources of DC power consist of one 20 cell 34-
ampere/hour battery and two 400ampere starter-
generators. DC power may be applied to the aircraft
through an external power receptacle on the right
nacelle. The starter-generators are controlled by
generator control units. The output of each generator
passes through a cable to the respective generator bus
(fig. 2-22). Other buses distribute por to aircraft DC
loads, and derive power from the generator buses. The
generators are paralleled to balance the DC loads
between the two units. When one of the generators is
not on line, aircraft DC power requirements continue to
be supplied from one of the other generators. Most DC
distribution buses are connected to both generator
buses but have isolation diodes to prevent power
crossfeed between the generating systems, when
connection between the generator buses is lost. Thus,
when either generator is lost because of a ground fault,
the operating generator will supply power for all aircraft
DC loads except those receiving power from the
inoperative generator's bus which cannot be crossfed.
When a generator is not operating, reverse current and
over-voltage protection is automatically provided. Two
inverters operating from DC power produce the required
single-phase AC power (figure 2-23). Three phase AC
electrical power for inertial navigation system and
mission avionics is supplied by two DC powered
inverters (figures 2-24 and 2-25).
2-72. DC POWER SUPPLY.
One nickel-cadmium battery furnishes DC power
when the engines are not operating. This 24-volt, 34-
ampere/hour battery, located in the right wing center
section, is accessible through a panel on the 2-58 top of
the wing. DC power is produced by two engine-driven
28 volt, 400-ampere starter-generators. Controls and
indicators associated with the DC supply system are
located on the overhead control panel (fig. 2-18) and
consists of a single battery switch (BATT), two generator
switches (#1 GEN and #2 GEN), and two volt-
Battery Switch. A switch, placarded BATT is
located on the overhead control panel (fig. 2-18) under
the MASTER SWITCH. The BATT switch controls DC
power to the aircraft bus system through the battery
relay, and must be ON to allow external power to enter
aircraft circuits. When the MASTER SWITCH is moved
aft, the BATT switch is forced OFF.
With battery or external power
electrical system, due to fault,
power cannot be restored to the
system until the BATT switch is
moved to OFF/RESET, then ON.
Generator Switches. Two switches (fig. 218),
placarded #1 GEN and #2 GEN are located on the
overhead control panel under the MASTER SWITCH.
The toggle switches control electrical power from the
designated generator to paralleling circuits and the bus
distribution system. Switch positions are placarded
RESET, ON and OFF. RESET is forward (spring-
loaded back to ON), ON is center, and OFF is aft.
When a generator is removed from the aircraft electrical
system, due either to fault or from placing the GEN
switch in the OFF position, the affected unit cannot have
its output restored to aircraft use until the GEN switch is
moved to RESET, then ON.
Master Switch. All electrical current may be
shut off using the MASTER SWITCH gangbar (fig.
2-18) which extends below the battery and generator
switches. The MASTER SWITCH gangbar is moved
forward when a battery or generator switch is turned on.
When moved aft, the bar forces each switch to the OFF