Oven will not heat | Main fan motor | Check for main fan operation. If fan is not |
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| operating, refer to "Oven fan will not run". |
| Air pressure switch | This normally open switch should close when |
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| the main fan is activated. Check air switch tube |
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| for blockage or obstructions. Adjust switch if |
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| necessary (see “Removal and installation” |
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| section for instructions). Replace air pressure |
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| switch as needed. |
| Temperature control | Check for supply voltage at temperature |
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| control. If no voltage is present, trace wiring |
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| back to air pressure switch. Turn the |
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| temperature adjustment knob to maximum |
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| temperature position and check for 230VAC at |
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| the load terminals #8 and neutral. If 230VAC is |
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| present and unit is not heating, refer to |
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| “Mercury contactor” for next check. If 230VAC |
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| is not present, proceed. |
| Thermocouple probe | With power on and thermocouple leads |
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| attached to the temperature control board: |
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| measure DC millivolt output of these leads. |
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| Refer to “Removal and installation” for proper |
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| readings. If these readings are not achieved, |
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| replace thermocouple. |
| Temperature control | Disconnect the potentiometer leads from the |
| potentiometer | control board. Place ohmmeter test leads on |
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| the blue and green pot. wires. Reading should |
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| be 1K ohms. Place meter leads across the blue |
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| and purple pot. leads and rotate knob from low |
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| to high. Repeat on green and purple leads. |
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| Check for an even rise and fall of ohms reading |
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| to insure that there are no open or dead spots |
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| in the potentiometer. Check each lead to |
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| ground for short circuits. Replace |
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| potentiometer as needed. |
| Mercury contactor | Check for supply voltage to the contactor coil. If |
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| voltage is present and the contactor will not |
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| activate, replace the contactor. Also, check |
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| each contactor for proper high voltage input |
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| and output. |
| Heater elements | Check the amp draw on each leg of the power |
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| supply for proper load. Check the oven |
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| specification plate for rating information. If the |
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| amp draw is low or high, check the individual |
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| elements for opens, shorts and proper |
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| resistance. WITH POWER OFF: To check |
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| resistance of the elements, remove all wires |
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| from the elements. The element resistance |
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| should be: |
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| 230VAC – 33 ohms approx. |
Oven heats with switch off | Mercury contactor | The mercury contactor has probably |
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| malfunctioned in the closed position. If there is |
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| no voltage to the operating coil, but there is |
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| high voltage at the contactor output, replace |
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| the mercury contactor. |
Intermittent heating | Thermal overload of main fan | The main fan motor is equipped with internal |
| motor | thermal protection and will cease to operate if |
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| overheating occurs. As the motor overheats |
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| and then cools, the heat circuit will cycle on |
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| and off intermittently. Improper ventilation or a |
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| lack of preventive maintenance may cause this |
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| condition. Also, most of the problems listed |
12 | Impinger II – | |