Compressor Checks - Friedrich Kuhl KCM21A30A Service Manual

Compressor Checks

WARNING
ELECTRIC SHOCK HAZARD
Turn off electric power before service or
installation.
All electrical connections and wiring MUST be
the National Electrical Code and all local codes
which have jurisdiction.
Failure to do so can result in personal injury or
death.
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 compressor. Restore power to unit.
Determine L.R.V.
Start the compressor with the volt meter 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 specified on the rating plate. If less than minimum, check for cause of inadequate power supply; i.e.,
incorrect wire size, loose electrical connections, etc.
Amperage (R.L.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 specification and performance 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 amperage on the meter. If the compressor does not start, the reading will indicate the locked
rotor amperage (L.R.A.).
Overloads
The compressor is equipped with either an external or 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 Overloads
CAUTION: Before attempting to check overloads, ensure that compressor is cool to touch.
External Overloads
With power off, remove the leads from compressor 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 overload is open and must be replaced.
Interrnal Overloads
Some model compressors are equipped with an internal overload. The overload is embedded in the motor windings to sense the
winding temperature and/or current draw. The overload is connected in series with the common motor terminal.
Should the internal temperature and/or current draw become excessive, the contacts in the overload will open, turning off the
compressor. The overload will automatically reset, but may require several hours before the heat is dissipated.
Checking the Internal Overload
1. With no power to unit, remove the leads from the compressor terminals.
2. Using an ohmmeter, test continuity between terminals
C-S and C-R. If no continuity, the compressor overload is open and the compressor must be replaced.
59
COMPONENT TESTING
WARNING
BURN HAZARD
Proper safety procedures must be followed,
and proper protective clothing must be worn
when working with a torch.
Failure to follow these procedures could
result in moderate or serious injury.