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 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.).
External Overload
Some compressors are equipped with an external 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 External Overload
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.
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 infinity (∞) between any two terminals MAY indicate an open winding. If, however, a reading of infinity
(∞)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 insufficient refrigerant charge, restriction in the refrigerant circuit, and excessive current draw.
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