TM 5-4310-354-14
indicated and replacement of the switch is
4-69. Engine Overspeed Switch.
required.
a. Removal. Disconnect the battery ground cable
and remove the overspeed switch transmitter unit as
(5) To test the switch for trip function, connect
shown in C, figure 4-35. Remove the overspeed switch
leads from a good transmitter to the
assembly as shown in figure 4-14.
switch.
Drive the transmitter with an
electric or air drill motor capable of
b. Testing. Off-unit testing of the overspeed switch
producing speed of at least 2250 rpm.
transmitter and overspeed switch is as follows:
When the transmitter is driven over 2250
rpm, the switch relay will open. After
(1) With transmitter removed from the engine
overspeed trip test, press reset button on
and the transmitter leads disconnected
circuit board to reset relay into closed
from the switch, using your fingers, check
mode.
for free turning of the transmitter drive tip.
(6) After testing, install overspeed switch
(2) Attach an ohmmeter across the two
cover, aligning tape (see para 4-69. b.(3)
transmitter leads. Turn the transmitter
above), and secure with four cover
drive tip. For each revolution of the drive
screws.
tip there should be four zero resistance
(on) and four resistance (off) events
c. Installation.
Install the overspeed switch
indicated on the ohmmeter. If there are
assembly as shown in figure 4-14. Install the overspeed
less than four on/off events, or the
switch transmitter as shown in C, figure 4-35. Connect
transmitter shows on or off only, it is not
the battery ground cable.
functioning properly and shall be replaced.
4-70.
Compressor
Oil
Temperature
Shutdown
(3) To test the overspeed switch, remove the
Switch.
four cover screws, noting a green tape
which indicates cover position for
a. Removal. Disconnect the battery ground cable
assembly.
The tape is an assembly
and remove the compressor oil temperature shutdown
reminder so that cover will not be
switch as shown in D, figure 4-35.
reversed; thereby, reversing terminal
labels.
b. Cleaning and Inspection.
(4) Make certain that the shorting bars across
(1) Wipe the shutdown switch with a clean,
the two terminals labeled "TACH" are
dry cloth.
secure.
Apply a 12 VDC (minimum)
power source having a minimum of 400
(2) Inspect the temperature probe for
ma to power terminals, noting polarity
distortion, cracks, breaks, damaged
requirement. When power is turned on
threads, and condition of plug connectors.
the relay coil should close, actuating the
microswitch mounted under the coil arm.
c. Installation.
Install the compressor oil
If the coil fails to actuate, a circuit failure is
temperature shutdown switch as shown in D, figure 4-35.
4-80
