Midco J83-DS - Manual (Page 9)

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The valve is a single function on-off type with automatic closing on current failure. Replace
entire valve if valve fails to open when power is applied or if leakage is defected on standby.
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The motor is a 1550 RPM shaded pole motor with auto-reset overload protection. It contains
a centrifugal Interlock Switch which is connected in the control circuit to prevent burner oper-
ation if the motor fails. The motor features permanently lubricated ball bearings and requires
no routine oiling maintenance.
„ Cleaning of the blower wheel is usually the only service required. Need for cleaning is
required if the inlet screen or blower wheel shows an accumulation of dust and lint. The motor
air cooling vents should also be cleaned at this time.
„ If the motor must be replaced, disconnect the motor wires from the burner terminal strip.
Remove the blower inlet screen and blower wheel and remove the motor case bolt nuts and
lockwashers.
„ When remounting the blower wheel, the distance from the wheel and the outside of the
blower housing air inlet side plate should be 5/16".
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The Thermal Switch is a heat sensitive single pole double throw snap switch that energizes
the blower motor to provide cooling air if, because of a heat back up through the burner when
the motor is off, the temperature of the blower housing reaches 160° F. The thermal switch
is not wired into the gas valve circuit and does not turn valve off when activated by heat back
up.
„ The switch mechanism is a bi-metallic disc that snaps over when it is heated to the set tem-
perature. The switch is mounted so that the disc bears against the side plate of the blower
housing.
„ Testing the switch to prove that it is functional can be done by removing the ignitor assem-
bly and blowing hot air through the opening toward the blower inlet. If hot air is not available,
remove the switch and check for continuity. With the switch cool, there should be continuity
between terminals 1 (black wire) and 3 (red/black wire). To simulate the “hot” condition, place
the switch on a firm surface and apply finger pressure to the switch disc. When the disc
“snaps”, there should be continuity between terminals 1 and 2 (red wire).
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The Electronic Control is a 24 volt AC, solid state electronic device that automatically ignites
and monitors the flame. It has an integral high voltage transformer and, upon flame startup,
applies high voltage to the spark electrode and 24V to the Main Automatic Gas Valve. When
the flame is proven, the spark is terminated and the burner run continues.
„ If the flame is not proven within 6 seconds, or if the proof of flame is lost during the burn-
er run and not re-established within 6 seconds, the Control will shut off the Main Automatic
Gas Valve and LOCK OUT. To reset the Control for restart, turn off the Burner Switch or
Timer for at least 30 seconds and then turn back on.
„ If the Electronic control is changed, the replacement must be identical as to the make and
model number, or must be an authorized substitute.
WARNING: Explosion hazard. Do not use this device if it gets wet. It can malfunc-
tion and cause serious injury or death. Replace any device that has been wet.
9
Part 1 Service
IX Main Automatic
Valve
X Blower Assembly
XI Thermal Switch
XII Electronic
Control System