TM 55-1510-219-10 2-48.  PROPELLER LEVERS. Two  propeller  levers  on  the  control  pedestal  (fig, 2-10),  placarded  PROP,  are  used  to  regulate  propeller speeds.    Each  lever  controls  a  primary  governor,  which acts    to    regulate    propeller    speeds    within    the    normal operation range.  The full forward position of the levers is placarded   TAKEOFF,   LANDING   AND   REVERSE   and also  HIGH  RPM.    The  full  aft  position  of  the  levers  is placarded  FEATHER.    When  a  lever  is  placed  at  HIGH RPM,   the   propeller   may   attain   a   static   RPM   of   2,000 depending   upon   power   lever   position.      As   a   lever   is moved aft, passing through the propeller governing range, but  stopping  at  the  feathering  detent,  propeller  RPM  will correspondingly  decrease  to  the  lowest  limit.    Moving  a propeller   lever   aft   past   the   detent   into   FEATHER   will feather the propeller. 2-49.  PROPELLER REVERSING. CAUTION Do  not  move  the  power  levers  into reverse   range   without   the   engine running.      Damage   to   the   reverse linkage mechanisms will occur. CAUTION Propeller  reversing  on  unimproved surfaces   should   be   accomplished carefully to prevent propeller erosion  from  reversed  airflow  and, in    dusty    conditions,    to    prevent obscuring the operator's vision. CAUTION To  prevent  an  asymmetrical  thrust condition,  propeller  levers  must  be in    HIGH    RPM    position    prior    to propeller reversing. The   propeller   blade   angle   may   be   reversed   to shorten landing roll.  To reverse, propeller levers must be positioned  at  HIGH  RPM  (full  forward),  and  the  power levers  are  lifted  up  to  pass  over  the  IDLE  detent,  then pulled  aft  into  REVERSE  setting.    One  yellow  caution light, placarded REV NOT READY, on the caution/advisory annunciator panel, alerts the pilot not to reverse  the  propellers.    This  light  illuminates  only  when the  landing  gear  handle  is  down,  and  if  propeller  levers are   not   at   HIGH   RPM   (full   forward).      This   circuit   is protected    by    a    5ampere    circuit    breaker,    placarded LANDING GEAR RELAY, located on the overhead circuit breaker panel (fig.  2-26). 2-50.  PROPELLER TACHOMETERS. Two tachometers on the instrument panel register propeller  speed  in  hundreds  of  RPM  (fig.    2-28).    Each indicator    is    slaved    to    a    tachometer    generator    unit attached to the corresponding engine. Section VII.  UTILITY SYSTEMS 2-51.  DEFROSTING/DEFOGGING SYSTEM. a. Description.    The  defrosting/defogging  system  is an  integral  part  of  the  heating  and  ventilation  system. The system consists of two warm air outlets connected by ducts to the heating system.  One outlet is just below the pilot's   windshield   and   the   other   is   below   the   copilot's windshield.      A   push-pull   control,   placarded   DEFROST AIR,  on  the  pilot's  subpanel,  manually  controls  airflow  to the windshield.  When pulled out, defrosting air is ducted to the windshield.  As the control is pushed in, there is a corresponding decrease in airflow. b. Automatic Operation. 1. Vent blower switches As required. 2. Cabin   temperature   mode   selector   switch AUTO 3. Cabin temperature  control As  required. 4. Cabin  air,  copilot  air,  pilot  air,  and  defrost air controls As required. c. Maximum Windshield Defrosting. 1. Pilot air, copilot air IN. 2. Cabin air and defrost air controls Out 3. Cabin         temperature         mode         selector switch MAN HEAT. 4. Cold air outlets As required. 5. Manual  temperature switch As  required. d. Manual  Operation.    If  the  automatic  temperature control should fail to operate, the tempera- 2-41