Midco International Inc.
9
8470 23
Service
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 operation 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
temperature. 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 assembly
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 fi rm surface and apply fi nger 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 fl ame. It has an integral high voltage transformer and, upon fl ame startup, applies high
voltage to the spark electrode and 24 V to the Main Automatic Gas Valve. When the fl ame is proven,
the spark is terminated and the burner run continues.
-
If the fl ame is not proven within 6 seconds, or if the proof of fl ame is lost during the burner 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 malfunction
and cause serious injury or death. Replace any device that has been wet.
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X Blower
Assembly
XI Thermal
Switch
XII Electronic
Control System
