Schreiber Engineering 300AC-MRI, Owner'S Manual

Page: 27 / 46

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 the
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 phase 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 indicates 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 problem. DO NOT reset the ground fault
protective device until you have located and corrected the problem. Refer to the Unit
Wiring Diagram and Service Manual 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.
22