TM 55-1510-219-10 ture   (of   defrost   air   and   cabin   air)   may   be   controlled manually    by    manipulating    the    CABIN    TEMP    MODE control    switch    between    the    OFF    and    MAN    HEAT positions. 2-52.  SURFACE DEICER SYSTEM. a. Description.    Ice  accumulation  is  removed  from each  inboard  and  outboard  wing  leading  edge,  and  both horizontal stabilizers by the flexing of deicer boots which are  pneumatically  actuated.    Engine  bleed  air,  from  the engine   compressor,   is   used   to   supply   air   pressure   to inflate  the  deicer  boots,  and  to  supply  vacuum,  through the  ejector  system,  for  boot  hold  down  during  flight.    A pressure regulator protects the system from over inflation. When  the  system  is  not  in  operation,  a  distributor  valve applies vacuum to the boots for hold down. CAUTION Operation    of    the    surface    deice system    in    ambient    temperatures below  -40°C  can  cause  permanent damage to the deice boots. b. Operation. (1) Deice   boots   are   intended   to   remove   ice after it has formed rather than prevent its formation.  For the  most  effective  deicing  operation,  allow  at  least  1/2 inch  of  ice  to  form  on  the  boots  before  attempting  ice removal.  Very thin ice may crack and cling to the boots instead of shedding. NOTE Never cycle the system rapidly, this may   cause   the   ice   to   accumulate outside  the  contour  of  the  inflated boots and prevent ice removal. (2) A   three   position   switch   on   the   overhead control  panel  placarded  DEICE  MANUAL  OFF  SINGLE CYCLE AUTO, controls the deicing operation.  The switch is   spring   loaded   to   return   to   the   OFF   position   from SINGLE CYCLE AUTO or MANUAL.  When the SINGLE CYCLE  AUTO  position  is  selected,  the  distributor  valve opens to inflate the wing boots.  After an inflation period of approximately 6 seconds, an electronic timer switches the  distributor  to  deflate  the  wing  boots  and  a  4  second inflation  begins  in  the  horizontal  stabilizer  boots.    When these   boots   have   inflated   and   deflated,   the   cycle   is complete. (3) If    the    switch    is    held    in    the    MANUAL position,  the  boots  will  inflate  simultaneously  and  remain inflated until the switch is released.  The switch will return to  the  OFF  position  when  released.    After  the  cycle,  the boots will remain in the vacuum hold down condition until again actuated by the switch. (4) Either     engine     is     capable     of     providing sufficient   bleed   air   for   all   requirements   of   the   surface deicer system.  Check valves in the bleed air and vacuum lines  prevent  backflow  through  the  system  during  single- engine  operation.    Regulated  pressure  is  indicated  on  a gage,   placarded   PNEUMATIC   PRESSURE,   located   on the copilots subpanel. 2-53.  ANTENNA DEICE SYSTEM. a. Description.  The antenna deice system removes ice  accumulation  from  the  inboard  wing  dipole  antennas and   the   aft   rotating   boom   dipole   antenna.      Pressure regulated bleed air from the engines supplies pressure to inflate the boots.  To assure operation of the system in the event    of    failure    of    one    engine,    a    check    valve    is incorporated  in  the  bleed  air  line  from  each  engine  to prevent  loss  of  pressure  through  the  compressor  of  the inoperative   engine.      Inflation   and   deflation   phases   are controlled    by    a    distributor    valve.        Deice    boots    are intended to remove ice after is has formed rather than to prevent   it's   formation.      For   the   most   effective   deicing operation, allow at least 1/8 to 1/4 inch of ice to form on the  boots  before  attempting  ice  removal.    Very  thin  ice may crack and cling to the boots instead of shedding. NOTE Never    cycle    the    system    rapidly. This may cause the ice to accumulate  outside  the  contour  of the  inflated  boots  and  prevent  ice removal. b. Antenna   Deice   System   Switch.      The   antenna deice  system  is  controlled  by  a  switch  placarded  ANT DEICE,  SINGLE-OFF-MANUAL  located  on  the  overhead control panel (fig.  2-18).  The switch is spring loaded to return to the OFF position from the SINGLE or MANUAL position.  When the switch is set to the single position, the system will run through one timed inflation-deflation cycle. When   the   switch   is   held   in   the   MANUAL   position   the boots  will  inflate  and  remain  inflated  until  the  switch  is released. c. Forward  Wide  Band  Data  Link  Antenna  Radome Anti-Ice.      The   forward   wide   band   data   link   antenna radome    anti-ice    system    utilizes    engine    bleed    air    to prevent the formation of ice on the radome. 2-42