Compressor Checks - Friedrich KUHL R-410A Service Manual

COMPRESSOR CHECKS

WARNING
ELECTRIC SHOCK HAZARD
Turn off electric power before service or
installation. Extreme care must be used, if it
becomes necessary to work on equipment with
power applied.
Failure to do so could result in serious 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 com-
pressor. 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 specifi ed 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 (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 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.
46
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
WARNING
ELECTRIC SHOCK HAZARD
Turn off electric power before service or
installation. Extreme care must be used, if it
becomes necessary to work on equipment
with power applied.
Failure to do so could result in serious injury or
death.
WARNING
BURN HAZARD
Certain unit components operate at
temperatures hot enough to cause burns.
Proper safety procedures must be followed,
and proper protective clothing must be
worn.
Failure to follow this warning could result
in moderate to serious injury.
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.