TM 9-4110-258-13
4.23 THERMOSTAT S3 OR SWITCH (HEATER LOCKOUT) S9 TESTING AND REPLACEMENT.
This task covers:
a. Testing
b. Removal
c. Installation
INITIAL SETUP
Materials/Parts:
Equipment Conditions:
Lock Washer (Clamp)
disconnected.
Self Locking Nuts (2)
Control box cover door raised and latched.
Tie Down Straps
General Safety Instructions:
Marker Tags (6)
WARNING
Silicone RTV
High voltage and exposed rotating parts are
Tape
used in the refrigeration unit. Personal injury
can result if power is connected.
a.
(1) Be sure power has been disconnected at the source and remove six screws (1).
(2) Carefully pull circuit breaker cover (2) out to expose thermostat (3) and switch (4) terminals.
(3) Remove screw (5), lock washer (6), and flat washer (7). Discard lock washer.
(4) Remove clamp (8).
(5) Immerse sensing bulb (9) into a temperature controlled bath at 32 F (0 C). A bath at this temperature
can be made by putting the sensing bulb into a container of ice and covering with water. Ice must remain
packed around sensing bulb at all times during tests.
(6) Using multimeter set to measure continuity, check thermostat (3) continuity between terminals A1 and A2
with thermostat setting at 24F (-4C) and at 40F (4C). Continuity should be indicated only when the
setting is at 24F (-4C). If continuity was indicated at 40F (4C) setting, replace thermostat.
(7) Using multimeter set to measure continuity, check thermostat (3) continuity between terminals B1 and B3
with thermostat setting at 24F (-4C) and at 40F (4C). Continuity should be indicated only when the
setting is at 40F (4C). If continuity was indicated at 24F (-4C) setting, replace thermostat.
(8) Remove sensing bulb (9) from temperature controlled bath.
(9) Adjust thermostat (3) to lowest temperature setting.
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