screw)   by   turning   screw   clockwise   to   decrease pressure     setting,     counterclockwise     to     increase pressure  setting.  Switch  must  be  adjusted  so  burner fuel  supply  cuts  off  should  pressure  drop  below  45 psi.  Burners  are  susceptible  to  flame  failure  should fuel pressure drop below 40 psi. 5-11.  Air Pressure Switch Adjustment (Refer to Fig C-13) a.  Remove electrical control box cover. b.  Remove air flow switch cover. c.  Start unit (turn on pump control switch). d.  Turn  on  low  fire  start  switch,  allow  low  fire burner to ignite. e.  Place obstruction in front of blower inlet. Hold obstruction over inlet for only a few seconds or until black smoke begins to emit from exhaust. If air flow switch is set properly, burner should be shut down. f.   If  burner  does  not  shut  down,  increase  setting of   air   flow   switch   by   turning   adjustment   screw clockwise. g.  Check   air   flow   switch   trip   point   again   by repeating step e in this paragraph. Repeat steps e and f  until   burner   shutdown   occurs   immediately   after obstruction  is  placed  over  blower  inlet.  If  switch setting  is  too  high,  burner  will  not  ignite  when  low fire switch is turned on. h.  Decrease    set    point    by    turning    adjustment clockwise until burner ignites. i.   Test air flow switch trip point after decreasing set point by repeating steps e and f j.   Replace switch cover. k.  Replace electrical control box cover. 5-12.  Low Water Pressure Switch Adjustment (Refer to Fig C-13) a.  Remove electrical control box cover. b.  Observe  settings  on  dial  indicator  of  switch, cut-in setting should be 20 psi, cut-out setting should be 5 psi. c.  If settings in step b are not as indicated, set cut- in  on  pressure  switch  (right  hand  screw)  by  turning screw clockwise to raise pressure setting, counterclockwise to decrease pressure setting. d.  Set cut-out on pressure switch (left hand screw) by   turning   screw   clockwise   to   decrease   pressure setting,     counterclockwise     to     increase     pressure setting. e.  Start unit and initiate low fire ignition. f.   After  low  fire  has  been  established,  shut  off water supply to water tank. Water tank should pump dry,  coil  back  pressure  and  outlet  pressures  drop  to zero psi and fire shut off. g.  If   fire   does   not   shut   off,   increase   cut-in setting slightly and repeat step f above until fire shuts off. h.  If switch setting is too high, fire will not ignite. Decrease    switch    setting    until    fire    ignites,    then perform  steps  f  and  g  of  this  paragraph  to  test  fire shut-off point. i.   Replace electrical control box cover. 5-13.  Excess Pressure Switch Adjustment (Refer to Fig C-13) a.  Remove electrical control box cover. b.  Observe  settings  on  dial  indicator  of  switch, cut-out   setting   should   be   350   psi,   cut-in   setting should be 150 psi. c.  If settings in step b of this paragraph are not as indicated, set cut-out on pressure switch (right hand screw)  by  turning  screw  clockwise  to  raise  pressure setting,     counterclockwise     to     decrease     pressure setting. d.  Set cut-in on pressure setting, coun- terclockwise to increase pressure setting. e.  Start   unit   and   develop   water   flow   through switch. f.   Slowly  close  discharge  valve(s)  and  observe pressure on coil outlet gage. g.  When  pressure  gage  reaches  350  psig,  motor should shut off. h.  When  pressure  drops  to  150  psig,  unit  motor should automatically restart. i.   If  motor  does  not  stop  and  start  at  pressures specified in steps g and h of this paragraph, readjust switch as indicated in steps c and d of this paragraph and retest until proper settings are achieved. j.   Replace electrical control box cover. 5-14.  Excess Temperature Switch (Refer to Fig C-13) a.  Remove electrical control box cover. b.  Set dial indicator on switch to 370°F. c.  Start  unit  and  initiate  high  fire,  two  gun,  300 GPH operational mode at 325°F. d.  After  ½  hour  operation  at  this  mode,  increase thermostat  setting  until  coil  outlet  temperature  gage reads 370°F. e.  If fire goes not trip, slowly decrease dial setting on switch until fire shuts off. f.   Allow temperature to drop and reset switch. g.  Fire unit at high fire to 370°F to see if switch cut-out setting repeats itself. h.  If setting does not repeat, perform steps e and f of this paragraph until proper setting is reached. i.   Replace electrical control box cover. TM 9-4940-342-14&P 35