TM 55-1510-219-10 quired to maintain the temperature selected by the cabin temperature control rheostat. (5)    Cabin   temperature   control   rheostat.      A control knob placarded CABIN TEMP INCR, located on the    overhead    control    panel    (fig.        2-18),    provides regulation     of     cabin     temperature     when     the     cabin temperature  mode  selector  switch  is  set  to  the  AUTO position,    or    the    A/C    COLD    OPN    position.        A    e temperature   sensing   unit   in   the   cabin,   in   conjunction with    the    setting    of    the    cabin    temperature    control rheostat,   initiates   a   heat   or   cool   command   to   the temperature controller for the desired cockpit or mission avionics compartment environment. (6) Manual   temperature   control   switch.      A switch placarded MANUAL TEMP INCR DECR, located on   the   overhead   control   panel   (fig.   2-18),   controls cockpit and mission avionics compartment temperature with  the  cabin  temperature  mode  selector  switch  set  to the   MAN   HEAT   positions.      The   manual   temperature control   switch   controls   cockpit   and   mission   avionics temperature by providing a means of manually changing the amount that the bleed air bypass valves are opened or closed.  To increase cabin temperature the switch is held    to    the    INCR    position.        To    decrease    cabin temperature,  the  switch  is  held  to  the  DECR  position. Approximately 30 seconds per valve is required to drive the   bypass   valves   to   the   fully   open   or   fully   closed position.  Only one valve moves at a time. (7) Forward vent blower switch.  The forward vent  blower  is  controlled  by  a  switch  placarded  VENT BLOWER AUTO LO HI, located on the overhead control panel (fig.  2-18).  In the auto position the fan will run at low  speed  except  when  the  cabin  temperature  mode selector  switch  is  set  to  the  OFF  position,  in  this  case the blower will not operate. (8) Aft   vent   blower   switch.      The   aft   vent blower  is  controlled  by  a  switch  placarded  AFT  VENT BLOWER   OFF   AUTO   ON,   located   on   the   overhead control   panel   (fig.      2-18).      The   single   speed   blower operates  automatically  through  the  cabin  temperature mode selector switch when the aft vent blower switch is placed    in    the    AUTO    position.        The    blower    runs continuously   when   the   switch   is   placed   in   the   ON position, In the OFF position, the blower will not operate. b. Automatic Heating Mode. 1. Bleed    air    valve    switches    OPEN, LEFT and RIGHT. 2. Cabin   temperature   mode   selector switch AUTO. 3.    Cabin  temperature  control  rheostat As required. 4. Cabin, cockpit and defrost air knobs As required c. Cabin Heating Mode. 1. Bleed    air    valve    switches    OPEN, LEFT and RIGHT. 2. Cabin   temperature   mode   selector switch MAN HEAT. 3. Vent blower switches As required. 4. Manual temperature switch As required. 5. Cabin, cockpit and defrost air knobs As required. 2-68.  AIR CONDITIONING SYSTEM. a. Description.    Cabin  air  conditioning  is  provided by   a   refrigerant   gas   vapor   cycle   refrigeration   system consisting of a belt driven, engine mounted compressor, installed  on  the  #2  engine  accessory  pad,  refrigerant plumbing,   N₁   speed   switch,   high   and   low   pressure protection  switches,  condenser  coil,  condenser  blower, forward  and  aft  evaporator,  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  circuit  breaker  placarded  AIR COND CONTR, located on the overhead circuit breaker panel (fig.  226), protects the compressor clutch circuit. (1) Forward evaporator. The forward evaporator   and   blower   supplies   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 switch, located on  the  overhead  control  panel  (fig.    2-18),  to  the  HI position.    The  forward  vent  blower  is  protected  by  a circuit   breaker   located   on   the   DC   power   distribution panel, located in the forward equipment bay. (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  mode.    The  rear  evaporator  supplies the   aft   ceiling   outlets,   rear   floor   outlets,   and   toilet compartment.  Rear evaporator blower is protected by a circuit   breaker   located   on   the   DC   power   distribution panel in the lower equipment bay. (3) High   and   low   pressure   limit   switches. High  and  low  pressure  limit  switches  are  provided  to prevent compressor operation beyond operational 2-55