b. Cleaning and Inspection.
Clean parts in a well-ventilated area. Avoid inhalation of solvent fumes and
prolonged exposure of skin to cleaning solvent. Wash exposed skin thoroughly.
Dry cleaning solvent (fed. spec. P-D-680) used to clean parts is potentially
dangerous to personnel and property. Do not use near open flame or excessive
heat. Flash point of solvent is 100° F (38° C).
(1) Clean the thermostats and flame switch with a clean, dry cloth. Clean all other parts with dry cleaning solvent
(fed. spec. P-D-680) and allow to dry.
(2) Inspect thermostats for cracks, dents, damage, and signs of overheating.
Check for loose or broken
terminals. Replace any damaged thermostats.
(3) Test the overheat thermostats (9 and 18) by connecting the terminals in series to a multimeter by heat
resistance, insulated wires. Place the thermostat in a heating chamber along with an accurate thermometer. Watch the
multimeter to determine the point at which thermostat opens. This must be between 263° and 277 °F (127° and 136°C).
Turn off heat and allow the thermostat to cool. It should close between 237 ° and 253°F (114 ° and 123°C). Replace the
thermostat if it fails to operate within these limits.
(4) Test safety switch (4) in a similar manner. Connect the switch terminals in series to a multimeter. Place the
switch in a heating chamber with an accurate thermometer. The thermostat must be open at approximately 110 °F (43°C).
Turn off the heat and allow the thermostat to cool. It should close at approximately 92 °F (33°C). Replace the thermostat
if it fails to open and close at these temperatures.
c. Installation. Installation is essentially the reverse of removal. Refer to figure 4-27 and note the following:
(1) If heater is mounted with discharge outlet up or discharge outlet down, be sure to install shield (16) on the
upper thermostat as shown. Failure to install the shield correctly may cause nuisance operation of the upper thermostat.
(2) If heater is mounted on either flat side, the shield should be mounted on the thermostat farthest from the
(3) When reinstalling flame switch, be sure that the end of the switch probe engages the bracket on the heat