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WARNING
DANGER OF BODILY INJURY OR DEATH
FROM ELECTRICAL SHOCK
When working on high voltage equipment - turn the
electrical power off before attaching test leads.
Use test leads with alligator type clips - clip to terminals,
turn power on, take reading - turn power off before
removing leads.
Compressor Checks
Locked Rotor Voltage (L.R.V.) Test
Locked rotor voltage (L.R.V.) is the actual voltage available
at the compressor under a stalled condition.
Single Phase Connections
Disconnect power from unit. Using a voltmeter, attach one
lead of the meter to the run "R" terminal on the compressor
and the other lead to the common "C" terminal of the com-
pressor. Restore power to unit.
CAUTION
Make sure that the ends of the lead do not touch the
compressor shell since this will cause a short circuit.
Determine L.R.V.
Start the compressor with the voltmeter attached; then
stop the unit. Attempt to restart the compressor within a
couple of seconds and immediately read the voltage on the
meter. The compressor under these conditions will not start
and will usually kick out on overload within a few seconds
since the pressures in the system will not have had time to
equalize. Voltage should be at or above minimum voltage
of 197 VAC, as specifi ed on the rating plate. If less than
mini mum, check for cause of inadequate power supply; i.e.,
incorrect wire size, loose electrical connections, etc.
Amperage (L.R.A.) Test
The running amperage of the compressor is the most
important of these readings. A running amperage higher
than that indicated in the performance data indicates that
a problem exists mechanically or electrically.
Single Phase Running and L.R.A. Test
NOTE: Consult the specifi cation and perform ance section
for running amperage. The L.R.A. can also be found on
the rating plate.
Select the proper amperage scale and clamp the
meter probe around the wire to the "C" terminal of the
compressor.
Turn on the unit and read the running am perage on the
meter. If the compressor does not start, the reading will
indicate the locked rotor amperage (L.R.A.).
External Overload
Some compressors are equipped with an exter nal overload
which senses both motor amperage and winding temperature.
High motor tempera ture or amperage heats the overload
causing it to open, breaking the common circuit within the
compressor.
Heat generated within the compressor shell, usually due
to recycling of the motor, is slow to dissipate. It may take
anywhere from a few minutes to several hours for the
overload to reset.
Checking the External Overload
With power off, remove the leads from com pressor
terminals. If the compressor is hot, allow the overload
to cool before starting check. Using an ohmmeter, test
continuity across the terminals of the external overload. If
you do not have continuity; this indicates that the over load
is open and must be replaced.
Internal Overload
Some compressors are equipped with an internal overload
which senses both motor amperage and winding temperature.
High motor temperature or amperage heats the overload
causing it to open, breaking the common circuit within the
compressor. Heat generated within the compressor shell,
usually due to recycling of the motor, is slow to dissipate. It
may take anywhere from a few minutes to several hours for
the overload to reset.
Checking the Internal Overload
A reading of infi nity (∞) between any two terminals MAY
indicate an open winding. If, however, a reading of infi nity
(∞) is obtained between C & R and C & S, accompanied
by a resistance reading between S & R, an open internal
overload is indicated. Should you obtain this indication,
allow the compressor to cool (May take up to 24 hours) then
recheck before condemning the compressor. If an open
internal overload is indicated, the source of its opening must
be determined and corrected. Failure to do so will cause
repeat problems with an open overload and/or premature
compressor failure. Some possible causes of an open internal
overload include insuffi cient refrigerant charge, restriction in
the refrigerant circuit, and excessive current draw.