START RELAY CHECKS AND MEASUREMENTS

StepExpected Result/Action
1. Check the compressor and/or motor nameplate for full load amps (FLA).Compressor full load amps are known.
Set up a clamp-on ammeter to measure AC current on the highest range
scale (higher than motor FLA). If using a digital clamp-on ammeter, use the
min./max. capability. Place the clamp-on ammeter around the wire that
connects the compressor start capacitor to the start relay contacts as shown in
Figure SP-9-13.
Equipment and test instruments prepared for measurement.
While watching the clamp-on ammeter, turn on the power. Observe the
current flow in the start capacitor circuit as the compressor motor starts. Turn
the power off after the observation is made.
At start-up, the clamp-on ammeter should momentarily indicate current flow,
then fall back to zero as the compressor comes up to speed. This shows that the
start relay is good because its contacts have opened, indicating that the relay coil
has energized. This happens very fast.
If the clamp-on ammeter continues to show current after the compressor comes
up to speed, the relay contacts have not opened, indicating the relay is bad and
should be replaced.
If no current is shown on the clamp-on ammeter, the relay contacts can be stuck
open, the related start capacitor has failed open, or the related wiring is open.
The condition of the start capacitor can be tested by performing steps 4 through 8
of this procedure.

pic1 5 START RELAY CHECKS AND MEASUREMENTS


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