TM 1-1510-223-10 Section VII.  UTILITY SYSTEMS 2-50. 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  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 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- 13).  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. 2-51. 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. Engine bleed air from the engine compressor 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 systerm Operation  of  the  surface  device  system  in ambient    temperatures    below    -40°C    can cause    permanent    damage    to    the    deice boots. NOTE Under    conditions    where    one    bleed    air source   is   inoperative,   sufficient   bleed   air pressure for deice boot inflation may riot be available.      Prior   to   deice   boot   inflation, check the regulated bleed air pressure gage for   a   minimum   of   16   PSI.      If   insufficient pressure exists, increasing engine N, and/or decreasing    aircraft    altitude    will    increase bleed air pressure. b. Operation. To  ensure  adequate  bleed  air  pressure  to the    deice    boots,    do    not    simultaneously actuate surface and antenna deice systems in the manual mode. (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 two position deice switch on the overhead control  panel  placarded  SURFACE  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 2-48