TM  9-2350-256-34-1 (a)  Inspect  the  flame  detector  switch  for cracks, heat distortion of the sensor tube, damaged terminals,  and  other  visible  damage.  Clean,  test,  and adjust the flame detector switch as described below. (b) Remove the adjusting screw and pivot the microswitch  on  its  bracket  to  provide  access  to  the ceramic rod. Invert the flame detector switch assem- bly  and  remove  the  ceramic  rod. (c) With the switch assembly inverted, rap on the side of the tube with a screwdriver blade to jar loose  oxides  and  dirt.  Continue  rapping  until  no more oxides fall out of the tube. (d)  If  the  operation  of  the  microswitch  is questionable,  test  it  for  continuity.  With  the microswitch  folded  back,  there  must  be  continuity across the NC contacts until the actuator on the bot- tom of the switch is depressed; then there must be continuity across the NO contacts. NOTE When the flame detector switch is assem- bled  and  properly  adjusted,  the  ceramic rod  depresses  the  actuator  to  close  the NO contacts. When the switch is at room temperature,   there   must   be   continuity across the NO contacts. (5)  Overheat  switch  (fig.  3-10.2).  Inspect  the contact  points  for  burning,  pitting,  scratches,  and other  damage.  Replace  the  overheat  switch  if  the points  are  defective. WARNING Do not attempt to bend the blade or the contact arm. Do not change the setting of the adjustment screw. (6) Fuel Control Valve (fig. 3-10.4). (a)  Clean   fuel   control   valve   parts   as   in- structed in paragraph 3-34f. (b) Inspect electrical parts for cracks, burned windings  or  leads,  signs  of  overheating,  and  other damage;  replace  damaged  parts. (c) Check the fit of the plunger assembly (34) in  the  sleeve  and  core  assembly  (28).  It  must  slide freely without excessive play. Check the sealing end of   the   plunger   for   scoring   or   damage;   replace damaged  parts. (d) Inspect the valve body for rough or scored seating surfaces, damaged threads, cracks, or other damage  replace  if  defective.  If  there  are  no  visible defects, check the heating element in the valve body as  follows: 1 Test equipment required: a.  24-volt  power  supply, 10  ampere minimum capacity. b.  Momentary  contact  switch. c. O to 10 ampere ammeter. 2 Connect the power supply ground lead to the  valve  body.  Connect  the  ammeter  between  the switch and the electrical terminal on the valve body. Connect power to the other side of the switch. 3 Close the momentary contact switch for a few seconds. Current as measured by the ammeter must be between 3.7 and 4.7 amps. CAUTION Do not apply current for longer than five seconds.   If   more   than   one   check   is required,  allow  10  minutes  cooling  time between tests. 4 If  heating  element  is  being  tested  with the thermostat still connected, and if current draw is less than 3.7 amps, the solder joint may be defec- tive. Repair it and retest. If it still fails, replace the fuel control valve as an assembly. 5 If amperage is greater than 4.7 amps, the heater  element  is  shorted.  The  fuel  control  valve must  be  replaced  as  an  assembly. (e) Check the electrical continuity through the solenoid coil assemblies (31). Continuity must exist. (f) Check the thermostat ( 17) for cracks, loose or  damaged  terminals,  and  distortion.  The  ther- mostat  must  close  when  temperature  is  reduced  to between  43°  and  57°F.  It  must  open  when  tem- perature  rises  to  between  65°  and  75°F.  If  ther- mostat operation is questionable, it can be checked using a multimeter set to the ohms function, while chilling the thermostat with ice. Do not immerse in- fluids.  Body  temperature  can  be  used  to  provide enought heat to warm it to above 75° F. to check the opening point. Replace a defective thermostat. (g) Inspect  all  other  parts  for  cracks,  distor- tion, corrosion, and other damage; replace damaged parts. (7) Ignition control (fig. 3-10.2). Inspect   the   ignition   control   assembly   (25)   for cracks,  loose  or  damaged  terminals,  or  other damage. Check for overheating or breaks in the elec- trical continuity path. Replace if defective. (8) Burner assembly (fig. 3-10.4). (a) If  the  heater  has  been  operation  for  400 hours or more since it was new or since the last bur- ner  replacement,  it  is  recommended  that  the  com- plete   burner   assembly   be   replaced.   After   this amount of use, distortion and erosion of the burner cup   and   the   fuel   vaporizer   shield   usually   make replacement  of  the  burner  advisable  to  ensure  ef- ficient combustion and maximum heat output. (b) Inspect the burner cup and stud assembly (14) and fuel vaporizer shield (12) for cracks, distor- tion, and erosion. Replace the complete burner as an assembly if the cup or shield is defective. (c) Inspect the plate and bushing assembly (4) for cracks, loose fuel feed bushing or igniter pocket, distortion,  erosion  of  holes,  and  other  damage. Change 2 3-18.15