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c) 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,
and 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 determined that temperature-sensing agent has leaked out,
and it must be replaced with a new thermostat.
d) Problems of motor and other electrical faults
i) Motor windings are damaged or there is a short circuited between turns
Analysis of Trouble
When motor windings are damaged or there the occurrence of a short circuit between turns,
the fuse will be blown repeatedly, and the blowout particularly occurs at that instance where
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 avometer. If short circuit occurs or the resistance of a
particular phase is low, this means that there is no short circuit in the windings and/or
between turns, and that insulation layers are damaged or deteriorated. Another instrument
that can also be used in this inspection is a megameter. If the insulation resistance is lower
than 2 MΩ, this means that the insulation layer has a breakdown already. If the motor is
damaged, repair or replaced it with a new one.
ii) Control relay is faulty
Analysis of Trouble
Overheating, burns or wearing of control relay contacts will generally occur if this is true. All
these will cause poor contact in electricity.
Remedy
Dismantle it for repairs, or replace it with a new one.
iii) Poor electric contractor in thermostat
Analysis of Trouble
Damaged contractor and leakage of temperature sensing agent will generally occur if this is
true.
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