TM 1-1510-223-10 (2)   The  CABIN  AIR  TEMP  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   AIR MODE SELECT switch in the MAN HEAT or MAN COOL position, regulation of the cabin temperature is accomplished   manually   with   the   CABIN   AIR   MANUAL TEMP switch (1)   In    the    MAN    HEAT    mode,    the    automatic system   is   overridden   and   the   system   is   controlled   by opening  and  closing  the  bypass  valves  (two)  CABIN  AIR MANUAL  TEMP  -  INCREASE  -  DECREASE  switch.    To increase    cabin    temperature,    hold    the    switch    in    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  AIR  MODE  SELECT  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  CABIN  AIR MANUAL TEMP  switch  in  DECREASE  position  for  approximately one minute to fully close air-to-air heat exchanger bypass valves. (3)   Bleed  air  entering  the  cabin  is  controlled  by LEFT   and   RIGHT   bleed   air   valve   switches   placarded ENVIRO   &   PNEU   BLEED   AIR   -   PNEU   ONLY   -   ON. When the switch is in the ON position, the environmental flow   control   unit   and   the   pneumatic   valve   are   open. When   the   switch   is   in   the   PNEU   ONLY   position,   the environmental    flow    control    unit    is    closed    and    the pneumatic  bleed  air  valve  is  open.    In  the  ENVIRO  & PNEU    BLEED    AIR    position,    both    are    closed.        For maximum cooling on the ground, turn the bleed air valve switches to the PNEU ONLY position. (4)   The  forward  vent  blower  is  controlled  by  the switch placarded VENT BLOWER FWD - AUITO - LOW - HIGH.  The 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 AIR MODE SELECT switch is placed in the OFF position.  In the OFF position, the blower will not operate. (5)      The   aft   vent   blower   is   controlled   by   the switch  placarded  VENT  BLOWER  AFT  -  AUTO  -  ON. The  single  speed  blower  operates  automatically  through the  N.    speed  switch  when  the  aft  vent  blower  switch  is placed   in   the   AUTO   position.      The   blower   operates continuously when the switch is placed in the ON position with  the  air  conditioner  compressor  running.    In  the  OFF position, the blower will not operate. Section IX.  ELECTRICAL POWER SUPPLY AND DISTRIBUTION SYSTEM 2-72  DESCRIPTION. The   aircraft   employs   both   direct   current   (DC)   and alternating    current    (AC)    electrical    power.        The    DC electrical   power   supply   (fig.      2-27)   is   the   basic   power system energizing most aircraft circuits.  Electrical power is  used  to  start  the  engines,  power  the  landing  gear  and flap  motors,  operate  the  standby  fuel  pumps,  ventilation blower,   lights,   and   electronic   equipment   AC   power   is obtained  from  the  DC  power  system  through  inverters. The single phase AC power system is shown in figure 2- 28,  and  the  three  phase  AC  power  system  is  shown  in figure  2-29.    The  three  sources  of  DC  power  consist  of one  20  cell  34-amperethour  battery  and  two  400-ampere starter-generators.      DC   power   may   be   applied   to   the aircraft   through   an   external   power   receptacle   on   the underside  of  the  right  wing,  just  outboard  of  the  nacelle. The starter-generators are controlled by generator control units.    The  output  of  each  generator  passes  through  a cable   to   the   respective   generator   bus.      Other   buses distribute power to aircraft DC loads, deriving power from the  generator  buses.    The  generators  are  paralleled  to balance the DC loads between the two units.  When one of  the  generating  systems  is  not  on  line,  and  no  fault exists,  all  aircraft  DC  requirements  may  be  supplied  by either   the   other   on-line   generating   system   or   by   an external power source.  The generator system is designed to  allow  cross  starting  of  the  other  engine.    When  one generator is on line, all current limiters are bypassed while starting the other engine.  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. Three phase AC electrical power for the inertial navigation 2-63