TM 1-1510-225-10 2-92 (2)   If the cockpit is too hot: 1.   CABIN AIR Knob – As required. 2.   PILOT and  COPILOT AIR Knobs  – In as required. 3.   DEFROST AIR Knob – In as required. b.  Cooling Mode. (1)   If the cockpit is too cold: 1.     PILOT and  COPILOT AIR Knob  – In as required. 2.     DEFROST AIR Knob – In as required. 3.     Overhead Cockpit Outlets – 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 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 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, 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. 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%.      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 switch. (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 LEFT     and 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.