2201Q4JE-MY-C9-N_2018.01.
Chapter 5 Maintenance and Inspection
Compound 2-stage Screw Compressor
4032**C
5.5 Reassembly
5-54
5.5.15.2 Micro-switches and Micro-switch Cam
The unloader indicator uses two micro-switches [125] and one micro-switch cam [127] to detect the
commanded 0% (30% for the high-stage) and 100% capacity control positions of the unloader slide
valve.
If the micro-switch fails or any of these connections becomes loose for some reason, correct position
detection cannot be made, and it causes a problem in the operation control of the compressor.
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Disassembly
Refer to Section 5.4.1 in this manual for the low-stage/high-stage disassembly procedure.
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Inspection
a) In the normal condition where the hydraulic line for the capacity control of the compressor is not
opened, set the unloader piston to the no load and full load positions from the manual capacity
control circuit and check the operation of the control circuit to see if the micro-switch can detect
the 0% (30%) and 100% positions of the micro-switch cam (i.e., by checking the operation of
the relevant relays and contacts).
If the hydraulic line for the capacity control of the compressor is opened for overhaul or other
work, use nitrogen gas or compressed air to set the unloader piston to the no-load and full load
positions and check if the micro-switch can detect the 0% (30%) and 100% positions of the
micro-switch cam.
b) After shutting down the control power and carrying out the lock-out and tag-out procedures,
remove the indicator glass and check that the micro-switch screws [126] are not loosened.
c) Check that the hexagon socket head set screw [128] securing the micro-switch cam [127] are
not loosened.
d) After checking that the wiring for the micro-switch has been removed, turn on and off the switch
to check the normal switching operation of the micro-switch using a circuit tester.
e) Carry out other visual inspection including any indication of water intrusion in the indicator, any
rust on switch terminals, any wear of the switch roller or micro-switch cam, and so on.
5.5.15.3 Reassembly
To carry out the reassembly, follow the disassembly procedure in reverse. Lastly, correctly set the
indicator needle (pointer) [138] position according to the following procedure:
a) If the hydraulic line for the capacity control of the compressor is opened for the purpose of overhaul
or other work, use nitrogen gas or compressed air to set the unloader piston to the no-load position.
Then, set and fix the indicator needle to the starting point of an illustration (on the indicator dial)
which indicates rotation. Next, set the piston to the full load position. Make sure the indicator
needle points to the end point of the range drawn on the dial.
b) In the normal condition where the hydraulic line for the capacity control is not opened, use the
manual capacity control circuit to move the piston.
While the control power is turned on, the indicator cover [146] must be mounted to prevent
possible electric shock.
Then, after the piston position is fixed, control power is turned off, and the lock-out and tag-out
procedures are completed, remove the indicator cover and secure the indicator needle in position.
