TM 1-1510-224-10 g. Forward Vent Blower Switch.    The  forward  vent blower    is    controlled    by    a    switch    placarded     VENT BLOWER  FWD  -  AUTO  -  LOW  -  HIGH,  located  on  the overhead   control   panel   (fig.      2-15).      In   the    AUTO position, the fan will run at low speed.  The forward vent blower   will   not   operate   when   the   cabin   temperature mode selector switch is set to the OFF position. h. Aft Vent Blower Switch.    The  aft  vent  blower  is controlled by the switch placarded  VENT  BLOWER  AFT - AUTO - ON, located on the overhead control panel (fig. 2-15).    The  single  speed  blower  operates  automatically through the N₁ 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  operating. In the OFF position, the blower will not operate. (1) Automatic heating mode. 1. BLEED   AIR   valve   switches   -   ON, LEFT and RIGHT. 2. CABIN  AIR  TEMP  MODE  SELECT switch - AUTO. 3. CABIN AIR TEMP CONTROL rheostat - As required. 4. CABIN, PILOT, COPILOT, and DEFROST AIR knobs - As required. (2) Manual heating mode. 1. BLEED   AIR   valve   switches   -   ON, LEFT and  RIGHT. 2. CABIN  AIR  TEMP  MODE  SELECT switch - MAN HEAT. 3. VENT    BLOWER    switches     -     As required. 4. CABIN  AIR  MANUAL  TEMP  switch - As required. 5. CABIN, PILOT, COPILOT, and DEFROST AIR knobs - As required. (3) Cargo  door  radiant  heat.    A  radiant  heat panel   is   provided   inside   the   cargo   door   to   provide supplemental  heating  in  the  aft  cabin  area.    The  heat panel    is    operating    whenever    the    cabin    temperature mode   switch   is   in   the   manual   heat   mode,   or   in   the automatic  mode  with  the  temperature  control  system  in the heat mode. 2-69.  AIR CONDITIONING SYSTEM. a. Description.  Cabin air conditioning is provided by   a   refrigerant-gas,   vapor-cycle   refrigeration   system (fig.  2-28).  The system consists of a belt-driven engine- mounted    compressor,    installed    on    the    #    2    engine accessory     section,     refrigerant     plumbing,     N,     speed switch,    high    and    low    pressure    protection    switches, condenser coil, condenser underpressure 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.    A  7.5-ampere  circuit breaker, placarded   AIR  COND  CONTR,  located  on  the overhead  circuit  breaker  panel  (fig.    2-9),  protects  the compressor clutch circuit. (1) Forward evaporator. The forward evaporator  and  blower  supplies  airflow  for  the  cockpit, forward  ceiling  outlets,  and  forward  floor  outlets.    The forward  evaporator  blower  has  a  high  speed,  which  can be selected by setting the  VENT BLOWER FWD switch, located on the overhead control panel (fig.  2-15), to the HIGH  position.    The  forward  vent  blower  is  protected  by a  circuit  breaker  located  on  the  DC  power  distribution panel, located beneath the aisleway. (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.      The   rear   evaporator   blower   is protected  by  a  circuit  breaker  located  on  the  DC  power distribution panel, located beneath the aisleway. (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  which  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.    The  blower  is  protected  by  a  50-ampere circuit  breaker  located  beneath  the  aisleway.    When  the cabin temperature mode selector switch is set to the  AC COLD 2-69