f. After   engine   is   running   allow   engine   to warm  up  a  minimum  of  5  minutes  at  1,100  ±  100  rpm (1,100 ± 100 r/min).  During warm-up do not allow engine speed to exceed 1,400 rpm (1,400 r/min).  This will avoid clutch plate drag. CAUTION If   compressor   oil   pressure   does   not register   within   5   seconds,   shut   down engine, and  determine  cause.    Refer  to TROUBLESHOOTING, (Section V). g. After   engine   is   warm,   engage   clutch   by pushing  clutch  handle  toward  panel  with  a   hard   fast thrust.      COMPRESSOR   OIL   PRESSURE   gauge   (5) should indicate oil pressure within five seconds. h. Pull  engine  THROTTLE  CONTROL  to  the full out position and lock by  turning  handle  in  clockwise direction until snug. WARNING Compressed   air   is   dangerous.      Make certain that service hoses to be used are not  frayed,  cracked,  or  deteriorated  in any way. 4-37. STARTING  UNDER  COLD  CONDITIONS  (5°F to 32°F) (-18°C to 0°C). a. If  ambient  temperature  is  between  5°F  (- 18°C)  and  32°F  (0°C),  press  and  hold  PUSHBUTTON GLO-PLUG switch (17) until heating coil glows red.  Do not hold longer than one minute. b. Make  certain  CLUTCH  handle   (11)   is   in disengaged position, away from control panel. c. Make certain  COMPRESSOR  UNLOADER switch  (16)  is  in  the  UNLOAD  position  and  close  all control panel valves. d. Make certain ENGINE THROTTLE CONTROL  (11)  is  positioned  half  way  in  (idle  position 1,100 ± 100 rpm [1,100 ± 100 r/min] ). e. Turn   MASTER   SWITCH   (9)   to   45°   cw position. CAUTION If  engine  oil  pressure  does  not  register on gauge within five seconds, shut down engine  and  determine  cause.    Refer  to Troubleshooting (Section V). f. Push   engine   START   switch   (8).      When engine   starts   continue   to   hold   START   switch   until ENGINE OIL PRESSURE gauge (6) registers pressure; then, release START switch. g. After   engine   is   running,   allow   engine   to warm  up  a  minimum  of  5  minutes  at  1,100  ±  100  rpm (1,100 ± 100 r/min).  During warm-up do not allow engine speed to exceed 1,400 rpm (1,400 r/min).  This will avoid clutch plate drag. CAUTION If   compressor   oil   pressure   does   not register   within   5   seconds,   shut   down engine, and  determine  cause.    Refer  to TROUBLESHOOTING, (Section V). h. After   engine   is   warm,   engage   clutch   by pushing  clutch  handle  toward  panel  with  a   hard   fast thrust.      COMPRESSOR   OIL   PRESSURE   gauge   (5) should indicate oil pressure within five seconds. i. Pull  engine  THROTTLE  CONTROL  to  the full out position and lock by  turning  handle  in  clockwise direction until snug. WARNING Compressed   air   is   dangerous.      Make certain that service hoses to be used are not  frayed,  cracked,  or  deteriorated  in any way. 4-38. STARTING UNDER EXTREME COLD CONDITIONS,  BELOW  5°F  (-15°C).    To  start  the  air compressor unit under extreme cold conditions, proceed as follows: a. The air compressor unit shall be preheated before operating in temperatures below 5°F (15°C). b. A   steady   flow   of   heated   air   should   be directed at the engine and air compressor for a minimum period of 30 min.  prior to starting the engine. c. Refer to para.  437 b.  through i. 4-39. STOPPING    PROCEDURE.        After    charging operation is completed, proceed as follows: a. Place    the    COMPRESSOR    UNLOADER (16, Figure 4-2) switch to the UNLOAD position. b. Unlock    and    push    ENGINE    THROTTLE CONTROL (10) to the idle position.  Disengage clutch by pulling CLUTCH handle (I ) away from control panel. 4-8