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Readings in the range listed below 100 Meg-Ohm would be an indicator that the system being tested may have
a contamination problem. Where does the problem come from? As an example, the filter drier may become sat-
urated and hold large percentages of moisture and the system function without a problem until such time as the
product operating conditions change. Should the room temperature increase, or the condenser plug-up etc., the
higher operating pressures and temperatures may cause the drier filter to release a portion of it’s held moisture.
It is also imperative to avoid opening the sealed refrigeration system whenever possible and when it is done to
be certain the true problem is correctly diagnosed and repaired. Remember, service gauge sets should only be
installed after all external checks have been performed.
CAUTION: Megger checks should NEVER be performed on any compressor that is under a
vacuum.
COMPRESSOR CONTACTOR
The contactor serves as the voltage supply switch for the compressor circuit. Voltage to the coil of the contactor
is supplied by the circuit board.
Check Out:
The two (2)* line supply screws of the contactor should always have supply voltage present when voltage is on
to the product.
The other two (2)* screws (load) should have line voltage when the contactor is energized. The contactor coil
receives its supply voltage from the circuit board. Should the contactor fail to energize:
Check for supply voltage from circuit board, lead connections to contactor coil, and ohms value of coil.
* (3) if the product is 3 phase
COMPRESSOR & STARTING COMPONENT CHECK-OUT PROCEDURE
When compressors fail to start or run properly, it is normally the external electrical supply or the compressor
start components that are defective -- the overload protector, start and/or run capacitor, relay, circuit board,
safety controls, etc.
1. Check voltage at compressor terminals. NO voltage will require checking the electrical circuit working back
from the compressor to determine where the voltage supply is interrupted and correct as required. The
load voltage, while compressor is trying to start, should not be less than 90% of rated required voltage.
Line voltage and wire size effect the life expectancy of the electrical components, compressor, motor winding,
solenoid coils, etc.
Poor line quality voltage will cause many erratic electrical problems. Remember every electrical product, ice ma-
chine, dispenser, walk-in, reach-in, air conditioner, etc. required proper power supply to operate. Be certain
when voltage checks are performed that you are measuring load voltage, not line voltage.
2. A defective capacitor or start relay may prevent the compressor from starting. Should the compressor at-
tempt to start, but is unable to do so, or if the compressor hums or trips off on the over protector, check the
following:
NOTE
:
For 50 HZ application on dual rated 50/60 HZ models, load voltage while compressor is start-
ing must not be less than 90% of 50 HZ
rating.
Relay
Potential --
For the potential type, contacts are normally closed. The start contacts open by C.E.M.F. generated by the com-
pressor at approximately 80% of the normal operating speed. As the contacts open, only the start capacitor is
removed from the start circuit. Both the start and run winding and the run capacitor remain in the circuit. This
relay may or may not be directional in mounting.
