Diagnostics and Troubleshooting
UNT-SVX041D-EN
83
Electric Heat with UC400-B Controller
Table 46. Electric heat does not energize
Probable Cause
Explanation
Unit wiring
The wiring between the controller outputs and the end devices must be present and correct for normal operation.
Refer to applicable wiring diagram.
Failed end device
Check the control contactors or the electric heat element, including any auxiliary safety interlocks, to ensure proper
operation.
No power to the controller
If the controller does not have power, heat outputs do not operate. For the controller to operate normally, apply
an input voltage of 24 Vac. If the Marquee/Power LED is
OFF
continuously, the controller does not have sufficient
power or has failed.
Diagnostic present
Several diagnostics affect electric heat operation. For detailed information about these diagnostics, refer to
Normal operation
The controller controls compressor or electric heat outputs as needed to meet the unit capacity requirements.
Unit configuration
The controller must be properly configured based on the actual installed end devices and application. If the unit
configuration does not match the actual end device, electric heat may not operate correctly.
Requested mode off
The user can communicate a desired operating mode (such as
OFF
, heat, and cool) to the controller. If
OFF
is
communicated to the controller, the unit shuts off the compressor or electric heat.
Freeze avoidance
When the fan is
OFF
with no demand for capacity (0%), and the outdoor air temperature is below the freeze
avoidance setpoint, the controller disables compressors and electric heat outputs (100%) to prevent coil freezing.
This includes unoccupied mode when there is no call for capacity or any other time the fan is
OFF
.
