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a) Check the input power circuit to see whether where is voltage of the
power supply, namely, the circuit which is connected to the knife switch.
This can be determined with an avometer or a test pencil. If a blown fuse is
found, ascertain and remove its cause, then replace it with a new one of
the same specifications.
b) Check the compressor accessories, including its thermal protector
and relay. In case the thermal protector is damaged, the compressor
cannot be powered on. If the relay is out of order, the motor will not run and
hum sound can be heard from it after the compressor is turned on, in that
case, shut it down immediately, otherwise, the motor windings will be
burned out in case this condition lasts longer.
c) Check the relay contacts and plugs to see if they are perfect and
work reliably. Poor contact may cause the motor not running or humming.
2) Check the circuit voltage to see whether it is normal.
Analysis of trouble
If the circuit voltage is obviously lower than its rated value, it will be
difficult to start the motor, and a hum sound can be heard from it.
Remedy
Measure the voltage with a voltmeter, if it is really too low, give
directions to the user for buying a stabilizer so as to step up the voltage,
thus normal operation can be achieved.
3) Check the thermal relay to see whether its contacts are closed.
Analysis of Trouble
The contacts of thermal relay sometimes may be open due to the
leakage of temperature sensing agent from the temperature sensor.
Remedy
Remove the relay cover to check up its contacts, if they are open, this
means that the original setting is not properly set or temperature sensing
agent has leaked out of the temperature sensor. Try to turn the adjusting
stem of this value in the direction of the lower temperature graduation, then
check the contacts to see whether they are closed. If they are still not
closed, dismantle the temperature sensing disc and then immerse it into
warm water to see whether the contacts actuate, if not, it can be
preliminarily determine that temperature sensing agent has leaked out, and
it must be replaced with a new thermostat.
4) Motor troubles and other electric faults
a) Motor windings have been burned or short-circuited between turns
Analysis of Trouble
When motor windings have been burned or short-circuited between
turns, the fuse will be blown repeatedly, and the blowout occurs particularly
at the instant when you close the knife switch.
Remedy
Check the terminals and the outer casing to see whether they are
short-circuited, and measure the resistance of each phase with an
Maintenance Service and Trouble Shooting