TM 1-1510-225-10 2-91 switches,   condenser   coil,   condenser   under-pressure switch, condenser blower, forward and aft evaporators, receiver-dryer,  expansion  valve,  and  a  bypass  valve.   The  plumbing  from  the  compressor  is  routed  through the  right  inboard  wing  leading  edge  to  the  fuselage and then forward to the condenser coil, receiver-dryer, expansion valve, bypass valve, and forward evaporator,   which   are   located   in   the   nose   of   the aircraft. (1)   Forward Evaporator. The forward evaporator and blower supplies airflow for the cockpit, forward  ceiling  outlets,  and  forward  floor  outlets.    The forward  evaporator  blower  is  controlled  by  a  switch placarded    VENT    BLOWER    HIGH    /    LO    /    AUTO, located on the copilot's subpanel. (2)   Aft  Evaporator.    The  aft  evaporator  and blower    are    located    in    the    fuselage    center    aisle equipment bay, aft of the rear spar.  Environmental air is circulated through the evaporator in either manual or automatic     control     modes.          The     rear     evaporator supplies  airflow  for  the  aft  ceiling  outlets,  rear  floor outlets, and toilet compartment. (3)   High  and  Low  Pressure  Limit  Switches.    High  and  low  pressure  limit  switches  are  provided  to prevent    compressor    operation    beyond    operational limits.    When  the  low  or  high-pressure  switches  are activated,   compressor   operation   will   be   terminated.   When  compressor  operation  has  been  terminated  by limit switch activation, the system should be thoroughly checked before returning it to service. (4)   Thermal Sense Switch.  A thermal sense switch  is  installed  on  the  forward  evaporator.    This sense   switch   actuates   a   hot   gas   bypass  valve  that bypasses a portion of the refrigerant from the forward evaporator, thereby preventing icing of the evaporator. (5)   Condenser  Blower.    A  vane-axial blower draws  air  through  the  condenser  when  the  aircraft  is on the ground. b.  Normal Operation. (1)   Automatic Coding Mode. 1.   BLEED    AIR    VALVES    Switches    – OPEN, LEFT and RIGHT. 2.   CABIN TEMP MODE Switch – AUTO. 3.   CABIN TEMP Rheostat – As required. 4.   CABIN, PILOT, COPILOT, and DEFROST AIR Knobs – As required. (2)   Manual Cooling Mode. 1.   BLEED    AIR    VALVES    Switches    – OPEN, LEFT and RIGHT. NOTE For  maximum  cooling  on  the  ground,  set the   BLEED   AIR   VALVES   switches   to   the ENVIR OFF position. 2.   CABIN  TEMP  MODE Switch   –  MAN COOL. 2-68.  UNPRESSURIZED VENTILATION. Ventilation   is   provided   by   two   sources.      One source is through the bleed air heating system in both the pressurized and unpressurized mode.  The second source   of   ventilation   is   obtained   from   ram   air   that enters  the  condenser  section  in  the  nose  and  passes through a check valve in the vent blower plenum.  The check    valve    closes    during    pressurized    operation.   Ventilation  from  this  source  is  in  the  unpressurized mode   only,   with   the    CABIN   PRESS  switch  in  the DUMP    position.        The    check    valve    closes    during pressurized operation. Ram air ventilation is distributed   through   the   main   ducting   system   to    all outlets.  Moving the ball in the socket can directionally control ventilation air ducted to each individual eyeball cold  air  outlet.    Regulate  the  volume  by  twisting  the outlet to open or close the valve. 2-69.  ENVIRONMENTAL CONTROLS. An environmental control section on the copilot's subpanel  provides  for  automatic  or  manual  control  of the    system.        This    section    contains    all    the    major controls  of  the  environmental  system:    bleed  air  valve switches,    forward    and    aft    vent    blower    switches, manual   temperature   switch   for   control   of   the   heat exchanger valves, cabin temperature level control, and the cabin temperature mode selector switch. a.   Heating Mode. (1)   If the cockpit is too cold: 1.   PILOT and  COPILOT AIR Knobs – As required. 2.   DEFROST AIR Knob – As required. 3.   CABIN  AIR  Knob  –  Pull  out  in  small increments.  Allow 3 to 5 minutes after each adjustment for system to stabilize.