Schreiber Chillers 15MEDAC email - Manual (Page 52)

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 unpaired 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 insulating breaks in the lead wires.
7. If #6 indicated 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.
8. Repeat #5 testing, carefully checking for ground, directly between each compressor terminal (C,
S, &R) and ground.
9. If once again a ground is indicated, proceed to properly replace the compressor, as it has failed
and cannot be repaired.
10. It is important to note that a volt-ohmmeter may be used only to check resistance and/or
continuity of the motor windings. This may be done as follows:
(a) For internal overload protected motor-compressor, the overload is located between the
common terminal of the compressor and the common motor lead inside the compressor.
If the resistance reading between Common and Start or Common and Run is open
(infinity) and the resistance reading between Start and Run indicates winding Resistance
Values in the Tecumseh Hermetic Compressor Service Data Book, then the internal
protector is open and time must be allowed for it to reset. Any Common and Start,
Common and Run, and Start and Run resistance reading must be within the values
shown in Tecumseh Hermetic Compressor Service Data Book. Three phases internal
overloads open all three phases. Therefore, allow time for reset.
(b) For external overload protected motor-compressors, the continuity of the overload may
be checked. The resistance of all winding may also be checked, i.e., C-S, C-R, and S-R.
(c) Any lack of continuity (other than test indicating an open internal protector) or improper
resistance, indicates a faulty or damaged motor and the compressor must be properly
replaced, as it has failed and cannot be repaired.
If the above indicated no problem with the compressor, then carefully reconnect the leads to the proper
compressor terminals (C,S, &R); correctly replace the terminal PROTECTIVE COVER, gasket (if
required), and the bale strap.
Then proceed to conduct similar ground and continuity test from the three lead connection points which
you previously, disconnected, forward toward the incoming power connections, to find the electrical
problems. DO NOT reset the ground fault protective device until you have located and corrected the
problem. Refer to the Unit Wiring Diagram and Service Manuel for the proper procedure and wiring
checkout.
The text of step-by-step procedures uses language and symbols which refer to the electrical supply as
single phase. Three-phase equipment should be given equally cautious consideration when service is
necessary.
Again, we want to stress that it is essential that WHENEVER ELECTRIC POWER is applied to the motor-
compressor, the terminal PROTECTIVE COVER must be properly in place.