TM 1-1510-223-10 air   conditioning   systems   are   automatically   controlled. Control   signals   from   the   temperature   control   box   are transmitted    to    the    bleed    air    heat    exchanger    bypass valves.    Here,  the  temperature  of  the  air  flowing  to  the cabin  is  regulated  by  the  bypass  valves  controlling  the amount of air bypassing the heat exchangers.  When the temperature of the cabin air has reached the temperature setting   of   the   cabin   temperature   control   rheostat,   the automatic temperature control allows hot air to bypass the air-to-air   exchangers   admitting   hot   air   into   the   cabin. When  the  bypass  valves  are  in  the  fully  closed  position, allowing  no  air  to  bypass  the  heat  exchangers,  the  air conditioner     begins     to     operate,     providing     additional cooling.      When   the   cabin   temperature   mode   selector switch   is   set   to   the   A/C   COLD   OPN   position,   the   air conditioning system is in continuous operation.  The cabin temperature control rheostat, in conjunction with the cabin temperature control sensor, provides regulation of cockpit and mission equipment compartment temperature.  Bleed air heat is added as required to maintain the temperature selected by the cabin temperature control rheostat. e. Cabin  Temperature  Control  Rheostat.    A  control knob   placarded   CABIN   AIR   TEMP   CONTROL   -   INCR located    on    the    overhead    control    panel    (fig.        2-13), provides  regulation  of  cabin  temperature  when  the  cabin temperature  mode  selector  switch  is  set  to  the  ALTO  or the AC COLD OPN position.  A 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 equipment compartment environment f. Manual  Temperature  Control  Switch.     A   switch placarded  CABIN  AIR  MANUAL  TEMP  -  DECREASE  - INCREASE located on the overhead control panel (fig.  2- 13), controls cockpit and mission equipment compartment temperature   with   the   cabin   temperature   mode   selector switch set to the MAN HEAT or MAN COOL position.  The manual  temperature  control  switch  controls  the  cockpit and    avionics    equipment    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. 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.  2-13).  In the ALTO 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 - AURO  -  ON,  located  on  the  overhead  control  panel  (fig. 2-13).    The  single  speed  blower  operates  automatically through the N] 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- 26).  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 under-pressure switch, condenser blower, forward and aft evaporators,    receiver-dryer,    expansion    valve,    and    a bypass valve. 2-60