TM 55-1510-220-10 2-12), 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 I)ECR 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 BI,OWER AUTO LO HI, located on the overhead control panel (fig.  2-12).  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.      2-12).      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  during  ground  operation and  the  air  conditioner  is  operating.    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. Manual heating mode. 1. Bleed   air   valve   switches   OPEN,   I,EFT and RIGHT. 2. Cabin  temperature  mode  selector  switch MAN HEA'I'. 3. Vent blower switches As required. 4. Manual temperature switch As required. 5. Cabin,  cockpit  and  defrost  air  knobs  As required. 2-69.  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  No.2  engine  accessory  pad,  refrigerant plumbing,   N1   speed   switch,   high   and   low   pressure protection   switches,   condenser   coil,   condenser-under- pressure   switch,   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  7  1/2-ampere  circuit  breaker  placarded  AIR COND  CONTR,  located  on  the  overhead  control  panel (fig.  2-12), 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.    2-12),  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 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 thoroughly checked before returning it to service. Change 2  2-56