| Control transformer | Check for 208/240VAC supply to the primary of the |
|
| control transformer. If no voltage is present, trace |
|
| wiring back to the main power switch. If voltage is |
|
| present, check for 24VAC at the transformer |
|
| secondary. If there is primary voltage, but no secondary |
|
| voltage, replace the control transformer. |
| Oven control | Check for 24VAC supply to control. If no voltage is |
|
| present, trace wiring back to control transformer. If |
|
| 24VAC is present, check for a |
|
| If there is 24VAC supplied, but there is no |
|
| the control display, replace the oven control. |
|
| If there is a |
|
| maximum temperature (see installation operations |
|
| manual for temperature adjustment). With the control |
|
| set at maximum temperature, check for supply voltage |
|
| to the oven control at terminals |
|
| is no voltage present, trace wiring back to the air |
|
| pressure switch. If there is voltage present, check for |
|
| output voltage at the Main heater relay (R1). If there is |
|
| voltage at the Main heater relay, proceed to “Main |
|
| heater relay” for next check. If there is no voltage at the |
|
| Main heater relay, trace wiring back to the oven control. |
|
| If there is no voltage output at the oven control, check |
|
| the |
|
| “PROBE FAIL”, this indicates that the thermocouple |
|
| has failed or become disconnected from the oven |
|
| control. |
| Thermocouple | Check to be sure that the thermocouple is securely |
|
| connected to the oven control. If the thermocouple is |
|
| connected to the oven control, and the control indicates |
|
| “PROBE FAIL”, disconnect the thermocouple from the |
|
| oven control and measure the resistance of the |
|
| thermocouple. The thermocouple should read approx. |
|
| 11Ω. If these readings are not achieved, replace the |
|
| thermocouple. If these readings are correct, proceed. |
| Oven control | If the thermocouple checks good, but the oven control |
|
| display indicates that there is a thermocouple failure, |
|
| replace the oven control. If the oven control indicates a |
|
| temperature reading but the oven will not heat, |
|
| proceed. |
| Thermocouple | WITH POWER ON AND THERMOCOUPLE |
|
| ATTACHED TO THE OVEN CONTROL: Measure the |
|
| DC millivolt output of the thermocouple. Refer to the |
|
| thermocouple chart (located in the “Removal” section of |
|
| the manual) for proper millivolt readings. If these |
|
| readings are not achieved, replace thermocouple. |
| Oven control | If the thermocouple checks good, but there is no |
|
| voltage output to the Main heater relay, replace the |
|
| oven control. If there is voltage output to the Main |
|
| heater relay, proceed. |
| Main heater relay | Check for supply voltage to the relay coil. If voltage is |
|
| present and the relay will not activate, replace the Main |
|
| heater relay. Also check each relay contact for high |
|
| voltage input and output. |
| 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 |
DTF – 1920 Series Service Manual | 7 |
