TM 1-1510-218-10 2-73 prefixed  to  the  digital  display  will  be  removed.    All event data is still available for playback until the data is erased.  The display will be prefixed with an "E" again on the next power up cycle if the old data has not been erased or if another event is recorded. NOTE Pressing  the  EXCEEDENCE  ERASE  switch for   0.2   seconds   or   longer   will   cause   all events    to    be    erased    from    non-volatile memory.      There   are   not   provisions   for erasing individual events.  The    Propeller    Speed    Tachometers    are    each protected  by  1.0-ampere  circuit  breakers  located  on the pilot’s left subpanel and placarded  PROP RPM  #1 and #2. Section VII.  UTILITY SYSTEMS 2-59.  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,  Figures  2-6 and  2-8,  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 switch – AUTO. 3.   Cabin Air Temp control  – As required. 4.   Cabin  air,  copilot  air,  pilot  air,  and  defrost air controls – As required. c.   Manual Operation. 1.   Pilot air, copilot air – In. 2.   Cabin air and defrost air controls – Out. 3.   Cabin air mode switch – MAN HEAT. 4.   Cold air outlets – As required. 5.   Cabin    air    manual    temp    switch    –    As required. 2-60.  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. 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 on the boots to form 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,      C    D    T1        and    DEICE MANUAL  SINGLE  CYCLE  AUTO    T2    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.