TM 9-4110-256-14
4-32. DEFROST TEMPERATURE SWITCH S4 TESTING AND REPLACEMENT.
This task covers:
a. Testing
b. Removal
c. Installation
INITIAL SETUP
Equipment Conditions:
General Safety Instructions:
Refrigeration unit shut down (para 2-7) and power
disconnected.
WARNING
Evaporator coil guard removed (para 4-18).
High voltage and exposed rotating parts are used in
Materials /Parts:
the refrigeration unit. Personal injury can result if
power is connected.
Marker tags (2)
7, Appendix E
Insulation Tape
10, Appendix E
a. Testing.
(1)
Remove insulation as necessary to expose defrost temperature switch (1).
(2)
Be sure power has been disconnected at the source then tag and disconnect two tabs (2).
(3)
Loosen two nuts (3), slide clamps (4) as necessary and remove defrost temperature switch (1).
Immerse defrost temperature switch (1) sensor surface plate into a temperature controlled bath at 500 F
(4)
(10C).
(5)
Using multimeter set to measure continuity, check defrost temperature switch (1) continuity between wire
lead terminals 2. No continuity should be indicated. If continuity was indicated, replace switch.
(6)
Carefully immerse defrost temperature switch (1) sensor surface plate only into a temperature controlled
bath at 20F (-7C).
(7)
Using multimeter set to measure continuity, check defrost temperature switch (1) continuity between wire
lead terminals (2). Continuity should be indicated. If continuity was not indicated, replace switch.
(8)
If no failure was indicated, install defrost temperature switch (1), slide two clamps (4) over switch, and
tighten nuts (3).
(9)
If tabs (2) or tab housing (5) are damaged, repair or replace.
(10) Using tags and wiring diagram (fig. 1-4), connect tabs (2). Remove tags.
(11) Install any insulation that was removed and wrap with insulation tape as necessary.
4-68
