TM 1-1510-223-10 (3)    Air conditioning cold operation mode.   (Used if ambient temperature is between 10°C and -25°C). NOTE Setting   the   cabin   temperature   mode   selector switch to the AC COLD OPN position at ambient temperatures   below   -25°C   may   cause   the   air conditioning  system  to  exceed  the  compressor low pressure limit setting, terminating compressor operation, and thereby rendering the system inoperative for the remainder of the flight 1. BLEED AIR valve switches - ON, LEFT and RIGHT. 2. CABIN AIR MODE SELECT switch - AC COLD OPN. 3. CABIN AIR TEMP CONTROL rheostat - As required. 4. CABIN, PILOT, COPILOT, and DEFROST air knobs - As required. 2-70. UNPRESSURIZED VENTILATION. Ventilation is provided by two sources.  One source is through    the    bleed    air    heating    system    in    both    the pressurized and unpressurized mode.  The second source of    ventilation    is    obtained    from    ram    air    through    the condenser  section  in  the  nose  through  a  check  valve  in the vent blower plenum.  Ventilation from this source is in the   unpressurized   mode   only   with   the   CABIN   PRESS DUMP  switch  in  the  DUMP  position.    The  check  valve closes  during  pressurized  operation.    Ram  air  ventilation is   distributed   through   the   main   ducting   system   to   all outlets.  Ventilation air, ducted to each individual eyeball cold  air  outlet,  can  be  directionally  controlled  by  moving the ball in the socket Volume is regulated by twisting the outlet to open or close the valve. 2-71. ENVIRONMENTAL CONTROLS. An  environmental   control   section   on'   the   overhead control panel (fig.  2-13) provides for automatic or manual control of the system.  This section contains all the major controls  of  the  environmental  system  including  bleed  air valve   switches,   forward   and   aft   vent   blower   switches, manual    temperature    switch    for    control    of    the    heat exchanger valves, a cabin temperature level control, and the cabin temperature mode selector switch for selecting automatic heating/ cooling or manual heating/cooling. a. Heating Mode. (1)   If the cockpit is too cold: 1. PILOT and COPILOT AIR knobs - As required. 2. DEFROST AIR knob - As required. 3. CABIN AIR knob - Pull out in small increments.  Allow 3 to 5 minutes after each adjustment for system to stabilize. (2)   If the cockpit is too hot: 1. CABIN AIR knob - As required. 2. PILOT and COPILOT AIR knobs - In as required. 3. DEFROST AIR knob - In as required. b. Cooling Mode: (1)   If the cockpit is too cold: 1. PILOT and COPILOT AIR knob - In as required. 2. DEFRIST AIR knob - In as required 3. Overhead cockpit outlets - As required. (2)   If the cockpit is too hot: 1. PILOT and C(OPILOT AIR knobs - Out as required. 2. CABIN AIR knob - Close in small increments.    Allow  3  -  5  minutes after each adjustment for system to stabilize.   If CABIN AIR knob is completely closed before obtaining satisfactory cockpit comfort, it may be necessary to place the AFT VENT BLOWER switch in the ON position to activate the aft evaporator to recirculate cabin air. c. Automatic Mode Control.   When the AUTO mode is selected on the CABIN AIR MODE SELECT switch, the heating   and   air   conditioning   systems   are   automatically controlled.      When   the   temperature   of   the   cabin   has reached  the  selected  setting,  the  automatic  temperature control     allows     heated     air     to     bypass     the     air-to-air exchangers  in  the  wing  center  section.    The  warm  bleed air is mixed with the cooled air.  The rear evaporator picks up recirculated cabin air only. (1)   When   the   automatic   control   drives   the environmental   system   from   a   heat   mode   to   a   cooling mode,  the  bypass  valves  close.    When  the  left  bypass valve   reaches   a   fully   closed   position,   the   refrigeration system  will  begin  cooling,  provided  the  right  engine  N, speed is above 650a When the bypass valve is opened to a     position     approximately     30° from     full     open,     the refrigeration system will turn off. 2-62