Check for proper voltage to the A421 Control.
- To remove the cover, loosen the two captive cover screws.
Use an AC voltmeter to check the voltage between the COM and 120 V or
240 V terminals on line-voltage models and the two 24 V terminals on
low-voltage models. See Figure 2.
Note: The voltage must be between:
- 20 VAC and 30 VAC for 24 VAC applications
- 102 VAC and 132 VAC for 120 VAC applications
- 177 VAC and 264 VAC for 208/240 VAC applications
- If the voltage reading is not within the required range, check the power source and input power wires for problems.
Check for proper sensor operation.
- Disconnect all power sources to the control.
- Use an accurate thermometer to take a temperature reading at the sensor location.
- Disconnect the sensor from the control.
- Use an ohmmeter to measure the resistance across the two sensor leads while the sensor is at the temperature taken in Step 2b.
- See Figure 1 to verify that the measured temperature and resistance conform to established temperature and resistance values.
- If the measured values conform to the values in Figure 1, proceed to Step 3.
If the sensor’s measured resistance value is substantially different
from the expected value for that temperature, check the sensor wiring.
If sensor wiring is correct, replace the sensor.
Figure 1. Temperature versus sensor resistance
Check the A421 for proper operation.
Note: Perform troubleshooting Steps 1 and 2 before you perform this step.
- Disconnect the load from the output relay terminals.
- Make sure that you install the Parameter Adjustments jumper so that you have unrestricted access to adjust parameters.
- Reconnect the sensor leads and supply power to the control.
- Replace the cover.
- Check the control settings for proper values.
- Press MENU until On appears. Press MENU again to display the On value.
Press Down or Up to
change the On temperature above and below the sensor temperature until
the relay energizes and de-energizes.
Note: If the anti-short cycle delay is set to a value other than 0 minutes, when the control is powered On, on the relay does not energize until the time delay elapses.
- If the output relay does not perform as expected, replace the A421 Control.
- If proper operation of the A421 Control is verified, reconnect the load and consult the equipment manufacturer’s instructions for troubleshooting the controlled equipment.