TM 1-1510-224-10 The engine  POWER  levers  actuate  an  engine  mounted cambox  which  is  connected  to  the  engine  fuel  control unit   (FCU)   and   the   propeller   reversing   cable.      The cambox  is  arranged  so  that  the  reversing  cable  is  not affected by  POWER  lever  movement  forward  of  the  idle stop.      When   the   POWER   levers   are   lifted   over   the reversing   detent   and   moved   rearward,   the   reversing cable  is  pulled  aft.    This  action  resets  the  beta  valve rearward,  allowing  the  governor  to  pump  more  oil  into the propeller, thus moving the blades through the ground fine range toward reverse pitch. As the blades move, the mechanical   feedback   collar   is   moved   forward.      This movement is transmitted by a carbon block on the end of the  reversing  lever  to  the  beta  valve,  causing  it  to  move forward.      As   the   POWER   levers   are   moved   further rearward (into the striped area), the propeller blades are moved   further   toward   the   reverse   pitch   stop,   and   the FCU is reset to increase engine speed. 2-48.  PROPELLER TACHOMETERS. Two  tachometers  on  the  instrument  panel  register propeller  speed  in  hundreds  of  RPM  (fig.    2-18).    Each indicator    is    slaved    to    a    tachometer-generator    unit attached  to  the  corresponding  engine,  installed  on  the reduction gearbox. Section VII.  UTILITY SYSTEMS 2-49.  DEFROSTING SYSTEM. a. Description.        The    defrosting    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 just below the copilot's windshield.      A   push-pull   control   placarded   DEFROST AIR, on the pilot's subpanel, manually controls airflow to the    windshield.        When    the    control    is    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 AIR MODE SELECT switch AUTO. 3. CABIN AIR TEMP CONTROL rheostat As required. 4. CABIN  AIR,  COPILOT  AIR,  PILOT  AIR, and  DEFROST AIR controls As required. c. Manual Operation.  If the automatic temperature control should fail to operate, the temperature of defrost air  and  cabin  air  can  be  controlled  manually  by  setting the   CABIN   AIR   MODE   SELECT   switch   to   the   MAN COOL  position,  then  using  the    CABIN   AIR   MANUAL TEMP   switch   to   set   the   desired   temperature.      This control is located on the overhead control panel (fig.      2-15).      Use   the   following   procedure   for   manual operation: 1. PILOT and  COPILOT AIR controls In. 2. CABIN AIR and  DEFROST  AIR controls - Out 3. CABIN    AIR    MODE    SELECT    switch    - MAN COOL. 4. Cold air outlets As required. 5. CABIN  AIR  MANUAL  TEMP  switch  -  As required. 2-50.  SURFACE DEICING SYSTEM. a. Description.    Ice  accumulation  is  removed  from each   inboard   and   outboard   wing   leading   edge,   both horizontal stabilizers, stabilons, and taillets by the flexing of deice boots which are pneumatically actuated.  Bleed air   is   used   to   supply   air   pressure   to   inflate   the   deice boots, and to supply vacuum through the ejector system. A   pressure   regulator   protects   the   system   from   over inflation.        When    the    system    is    not    in    operation,   a distributor  valve  keeps  the  boots  held  down  by  vacuum supplied through the ejector system. CAUTION Operation of the surface deice system in ambient temperatures below   -40°C   can   cause   permanent damage to the deice boots. 2-56