TM 1-1510-225-10 2-88 their normal inoperative position and stop.  Turning the switch only to the OFF position will stop the windshield wipers,  without  returning  them  to  the  normal  inactive position. 2-63.  CHEMICAL TOILET. a.   Description.    A   side-facing  chemical  toilet, which   can   also   be   used   as   an   additional   seat,   is installed  in  the  aft  cabin  area.    Two  hinged-lid  half- sections  must  be  raised  to  gain  access  to  the  toilet.   Waste  is  stored  within  a  removable  container  located below  the  seat  in  the  cabinet  assembly.    This  non- flushing  system  uses  a  dry  chemical  preparation  to deodorize the stored waste.  A toilet tissue dispenser is contained in a slide-out compartment on the forward side    of    the    toilet    cabinet    assembly.        A    box    of disposable    waste    container    liners    and    a    box    of chemical   deodorant   packets   are   also   stored   in   the cabinet. b.  Operation. During use, a removable throwaway    plastic    liner    is    attached    to    the    waste container.  After use, dry chemical deodorant obtained from the storage cabinet is deposited on the waste and the  hinged  lid  sections  are  closed  over  the  cavity.   After     each     flight,     the     waste     container     must     be removed,     emptied,     relined,     and     replaced     in     the cabinet.        Consumable    toilet    items    should    be    re- supplied as needed. 2-64.  ELECTRICAL TOILET  T3  F3 . A side-facing toilet is located opposite the airstair door.    A  curtain  is  provided  which,  when  extended across   the   passenger   compartment,   separates   the toilet    area.        The    seat    may    also    be    used    as    a passenger seat. The  toilet  is  a  re-circulating  electric  flush  type.   Normal servicing is within 2-1/2  gallons  of  fluid,  which provides    for    approximately    15    uses.        When    the container    is    removed    for    servicing,    it    is    sealed.   Chemical is mixed with water in a ratio of 3 ounces to 2 quarts of water. Power   for   the   electric   flush   motor   is   provided through    either    the    FURN    ON    or     COFFEE    OFF positions   of   the   furnishings   switch   located   on   the copilot's inboard side panel. Also located in a storage area along the fuselage wall    is    a    relief    tube.        A    lever    type    handle    is incorporated which, when pressed, allows suction from outside air to draw  waste  overboard  through  the  relief tube drain. 2-65.  SUN VISORS. CAUTION When  adjusting  the  sun  visors,  grasp  only by    the    top    metal    attachment    to    avoid damage to the plastic shield. Individual  sun  visors  are  provided  for  the  pilot and copilot.  Each visor is manually adjustable.  When not needed as a sun shield, each visor may be rotated to a position flush with the top of the cockpit so that it does not obstruct view through the windows. Section VIII.  HEATING, VENTILATION, COOLING, AND ENVIRONMENTAL CONTROL SYSTEM 2-66.  HEATING SYSTEM. Warm  air  for  heating  the  cockpit  and  cabin  and for  defrosting  the  windshield  is  provided  by  bleed  air from both engines.  Engine bleed air is combined with ambient   air   in   the   heating   and   pressurization   flow control unit in each engine nacelle.  If the mixed bleed air is too warm for cockpit comfort, it is cooled by being routed through an air-to-air heat exchanger located in the forward portion of each inboard wing.  If the mixed bleed     air     is     not     too     warm,     the     air-to-air     heat exchangers are bypassed.  The mixed bleed air is then ducted   to   a   mixing   plenum,   where   it   is   mixed   with cabin re-circulated air.  The warm air is then ducted to the  cockpit  outlets,  windshield  defroster  outlets,  and floor     outlets     in     the     cabin     compartment.          The environmental system is shown in Figure 2-26. a.   Bleed  Air  Flow  Control  Unit.    A  bleed  air flow control unit, located forward of the firewall in each engine  nacelle,  controls  the  flow  of  bleed  air  and  the mixing of ambient air to make up the total airflow to the cabin for heating, windshield defrosting, pressurization, and ventilation. The unit is electronically     controlled     with     an     integral     electric solenoid    firewall    shutoff    valve,    controlled    by    the BLEED AIR VALVES switches located on the copilot's subpanel,     and     a     normally     open solenoid valve operated by the right landing gear safety switch. b.  Pneumatic   Bleed   Air   Shutoff   Valve.      A pneumatic  shutoff  valve  is  provided  in  each  engine nacelle  to  control  the  flow  of  bleed  air  to  the  surface and brake deice systems.  The  BLEED  AIR  VALVES  switches,   located   on   the   copilot's   subpanel,   control these valves.