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DTF – 1920 Series Service Manual
2
SEQUENCE OF OPERATION
DUAL TECHNOLOGY FINISHER
1921 208VAC 60 HZ. 3 PHASE
1922 240VAC 60 HZ. 3 PHASE
POWER SUPPLY Electrical power to be supplied to the oven by a four conductor service for three phase.
Black conductor is hot.
Red conductor is hot.
Orange conductor is hot
Green conductor is ground.
MAIN FAN CIRCUIT Power is permanently supplied through the 10 amp fuses, through the normally closed
oven cavity hi-limit thermostat, to the normally open main power switch and to terminal
number 1 of the 30 minute cool down timer. Closing the main power switch enables the
30 minute cool down timer. The 30 minute cool down timer supplies line voltage to the
coil of the main fan relay, its contacts now close, supplying 208/240VAC to the main fan
motor. Voltage is also supplied to the primary of the control transformer, the conveyor
motor, the oven control and the infrared heater switch.
NOTE: Model 1922 ovens use a 240VAC to 208VAC step down transformer for the
main fan motor
TEMPERATURE CONTROL Closing the main power switch supplies 208/240VAC to the primary of the control
transformer. Secondary voltage, 24VAC, is supplied to the oven control. The oven
control is set to desired temperature. The thermocouple will provide varying millivolts to
the oven control. The oven control supplies 208/240VAC to the coil of the heater relay at
intermittent intervals to maintain the desired temperature. The display on the oven
control will indicate when the main heater relay is energized.
NOTE: The display also indicates oven temperature.
INFRARED HEAT Closing the infrared heater switch supplies line voltage to the coil of the infrared heater
relay, its contacts now close, supplying 208/240VAC to the infrared heaters.
CONVEYOR DRIVE Closing the main power switch supplies 208/240VAC to the primary of the control
transformer and, through the air pressure switch, the Infrared heater switch, to the
conveyor motor. Secondary voltage, 24VAC, is supplied to the oven control. Setting the
oven control to the desired time outputs voltage, through a reversing switch and
capacitor, to the conveyor motor.
NOTE: The conveyor system uses a hall effect sensor and magnet to prove operation of
the conveyor motor. If the conveyor motor is not running, “BELT JAM” is indicated on
the display.
AUTOMATIC COOL DOWN When the machine is started, the time delay relay timing circuit is enabled, permitting
the main fan to operate for approximately 30 minutes after the machine is shut off, to
cool the machine. The 30-minute time delay relay will keep the coil of the main fan relay
energized, maintaining operation of the main fan motor for 30 minutes.