TM 1-1510-225-10 2-81 serves    both    the    surface    deice    system    and    the pneumatic systems operation. b.  Operation.      A    switch,    placarded    BRAKE DEICE,  located  on  the  pilot's  subpanel  controls  the solenoid   valve   by   routing   power   through   a   control module  box  under  the  aisle  floorboards.    A  5-ampere circuit  breaker,  placarded  BRAKE  DEICE, located on the   right   sidewall   circuit   breaker   panel   protects   the system.    A  timer  limits  operation  to  approximately  10 minutes  to  avoid  excessive  wheel  well  temperatures when   the   landing   gear   is   retracted.      The   control module  also  contains  a  circuit  to  the  green   BRAKE DEICE   ON  annunciator,   and   has   a   resetting   circuit interlocked  with  the  gear  uplock  switch.    When  the system is activated, the BRAKE DEICE ON annunciator    should    be    monitored    and    the    control switch selected OFF after the annunciator extinguishes,  otherwise,  on  the  next  gear  extension, the system will restart without pilot action.  The control switch should also be selected  OFF if deice operation fails  to  self-terminate  after  approximately  10  minutes.   If   the   automatic   timer   has   terminated   brake   deice operation  after  the  last  retraction  of  the  landing  gear, the landing gear must be extended in order to obtain further operation of the system. NOTE The  BL  AIR  FAIL  annunciator  lights  may illuminate momentarily during simultaneous operation of the surface and brake  deice  systems  at  low  N₁  speed.    If lights extinguish immediately they may be disregarded. (1)   During certain ambient conditions, use of the  brake  deice  system  may  reduce  available  engine power,  and  during  flight  will  result  in  an  ITT  rise  of approximately  20 °C.    Applicable  performance  charts should be consulted before brake deice system use.  If specified power cannot be obtained without exceeding limits, the brake deice system must be selected   OFF until  after  takeoff  is  completed.    ITT  limitations  must also be observed when setting climb and cruise power.   The  brake  deice  system  is  not  to  be  operated  above 15    °C    ambient    temperature.        During    periods    of simultaneous brake deice and surface deice operation, maintain  85%  N₁  or  higher.    If  inadequate  pneumatic pressure  is  developed  for  proper  surface  deice  boot inflation,  select  the  brake  deice  system   OFF.    Both sources  of  pneumatic  bleed  air  must  be  in  operation during brake deice system use.  Select the brake deice system OFF during single engine operation. 2-58.  FUEL SYSTEM ANTI-ICING. a.   Description.    An  oil-to-fuel  heat  exchanger, located    in    each    engine    accessory    case,    operates continuously    and    automatically    to    heat    the    fuel sufficiently to prevent freezing of any water in the fuel.   No controls are involved.  Three external fuel vents are provided  on  each  wing.    One  is  recessed  to  prevent ice formation, the second is flush mounted so that no ice   can   collect   upon   it,   and   the   third   is   electrically heated.  Heating is controlled by two toggle switches, placarded FUEL  VENT  LEFT and  RIGHT, located on the   pilot's   subpanel.      They   are   protected   by   two 5-ampere    circuit    breakers,    placarded    FUEL    VENT LEFT and  RIGHT,  located  on  the  right  sidewall  circuit breaker panel. CAUTION To prevent overheat damage to electrically heated   anti-ice   jackets,   the   FUEL  VENT heat   switches   should   not   be   turned   on unless  cooling  air  will  soon  pass  over  the jackets.  b.  Normal   Operation.    For  normal  operation, switches for the fuel vent anti-ice circuits are turned on as required during the BEFORE TAKEOFF procedures. 2-59.  WINDSHIELD   ELECTROTHERMAL   ANTI-ICE SYSTEM. a.   Description.    Both  the  pilot’s  and  copilot's windshields  are  provided  with  an  electrothermal  anti- ice system.  Each windshield is part of an independent electrothermal    anti-ice    system.        Each    system    is comprised   of   the   windshield   assembly   with   heating wires sandwiched between glass panels, a temperature sensor attached to the glass, an electrothermal controller, two relays, a control switch, and   two   circuit   breakers.      Two   switches,  placarded WSHLD  ANTI-ICE  PILOT  NORMAL  /  OFF  /   HIGH, and  WSHLD  ANTI-ICE  COPILOT,  NORMAL /  OFF / HIGH, located on the pilot's subpanel, control system operation.    Each  switch  controls  one  electrothermal windshield system.  A 5-ampere circuit breaker   and a 50-ampere circuit breaker, which are not accessible to the flight crew, protect the circuits of each system. CAUTION To     help     prevent     windshield     cracking, windshield   heat   should   be   placed   in   the NORMAL  position  for  at  least  15  minutes prior to using the HIGH position. b.  Normal  Operation.    Two  levels  of  heat  are provided through the three position switches, placarded  NORMAL  in  the  up  position,   OFF  in  the center position, and HIGH after pulling the switch over a  detent  and  moving  it  to  the  down  position.     In  the