Schreiber Chillers Old 4 ton MRI - Manual (Page 26)

Hermetic compressors can be properly serviced without unnecessarily removing the
terminal PROTECTIVE COVER by adhering to the following service procedures:
1.
If the branch circuit, short circuit, and ground fault protective device, i.e., fuse or
circuit breaker, is open, this is a strong indication that an electrical problem exists
and must be found and corrected.
The circuit protective device rating must first be checked as required by the
National Electrical Code, and its maximum rating should coincide with that marked
on the equipment nameplate and/or on the unit wiring diagram and/or instructions.
This breaker or fuse rating should be as low as practical. A rule of thumb is 175%
times the motor-compressor RLA (FLA on older units) as shown on the unit
nameplate.
It is acceptable to first replace the fuse or reset the circuit breaker ONE TIME to
determine if it was just a nuisance opening. WARNING! The terminal
PROTECTIVE COVER must be securely in place.
2.
If the fuse or circuit breaker again opens, DO NOT continue to replace or reset, as
the equipment obviously has an electrical problem. CAUTION! Continual resetting
may cause the terminal to vent.
3.
DISCONNECT all power to the unit, making sure all power legs are open.
4.
Without removing the terminal PROTECTIVE COVER, disconnect the three leads
going to the compressor terminals at the nearest point to the compressor, and
identify them as Common (C), Start (S), and Run (R). Identification can generally
be made through the unit-wiring diagram. DO NOT disconnect at the compressor
terminals at this time.
5.
With a Megger, Hi-Potential Ground Tester, or other suitable instruments which
puts out a voltage between 300 and 1500 volts, check for a ground separately
between each of the three C, S, & R leads and ground (such as an unpainted tube
on the compressor). Do not use a low voltage output instrument such as a volt-
ohmmeter or other such continuity instruments, as these will not detect a low level
fault (ground).
6.
If a ground is indicated, then carefully remove the compressor terminal
ROTECTIVE COVER and inspect for loose leads or insulation breaks in the lead
wires.
7.
If #6 indicates no visible problem, carefully remove the leads at the compressor
terminals. CAUTION: Damage can occur to the glass embedded terminals at this
point if the leads are not properly removed, which can result in the terminal venting
and hot oil discharging. No ignition, however, can occur if all power is
disconnected and no external ignition source is present.
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