(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.
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.
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
(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
1 Test equipment required:
a. 24-volt power supply,
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.
Do not apply current for longer than five
seconds. If more than one check is
required, allow 10 minutes cooling time
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
(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.