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DTF – 1920 Series Service Manual
8
a digital multimeter.
The element resistance should be as follows:
208V – 43 ohms approx.
240V – 57 ohms approx.
Replace heating elements as needed.
No Infrared Heating Main fan motor Check for main fan operation. If it is not operating, refer
to “Oven fan will not run”.
Air pressure switch Check for 208/240VAC to the air pressure switch. If no
voltage is present, trace wiring back to main power
switch. This normally open switch should close when
the main fan is activated. Refer to the “Removal and
installation” section for proper adjustment. Replace as
needed.
Switch, Infrared heater Check for 208/240VAC to the Infrared heater switch. If
no voltage is present, trace wiring back to the air
pressure switch. WITH POWER OFF: Check continuity
between switch terminals. Replace switch as needed.
Infrared heater relay Check for supply voltage to the relay coil. If no voltage
is present, trace wiring back to Infrared heater switch. If
voltage is present and the relay will not activate,
replace the Infrared heater relay. Also check each relay
contact for high voltage input and output.
Infrared Heating element(s) Check the Amp draw on each power leg for proper
load. Check the specification plate for rating
information. If the amp draw is high or low, check the
individual elements for opens, shorts and proper
resistance.
WITH POWER OFF: To check resistance of the
elements, remove all leads from the elements and use
a digital multimeter.
The element resistance should be as follows:
208V – 45 ohms approx.
240V – 58 ohms approx.
Replace heating elements as needed.
Oven heats with switch off Main heater relay or
Infrared heater relay
The Main heater relay or Infrared heater relay has
probably failed in the closed position. If there is no
voltage to the operating coil, but there is high voltage at
the relay output, replace the heater relay.
Intermittent heating Thermal/overload of motor The main fan motor is equipped with internal thermal
protection and will cease to operate if overheating
occurs. As the motor overheats and then cools, this will
cause the oven to cycle on and off intermittently.
Improper ventilation or lack of preventive maintenance
may cause this. Also, most of the problems listed under
“Oven will not heat” can cause intermittent failure.
Conveyor will not run NOTE: Display will indicate
“Belt Jam”
Power supply Check circuit breakers, reset if required. Check power
plug to be sure it is firmly in receptacle. Measure
incoming power, call power co. if needed.
Fuse, 10 Amp Check, replace if necessary.
Fuse holder Check, replace if necessary.
Hi-limit thermostat, oven cavity
Terminals are normally closed. If open, reset
thermostat and retest. If thermostat will not hold for
maximum oven temperature, and oven is not exceeding
temperature setting, check for proper location of
capillary bulb in its spring holder. If the capillary checks
okay, replace the hi-limit thermostat.