BCX-SVX002A-EN
137
Table 58. DX or electric heat does not energize (continued)
Probable Cause Explanation
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 DX and 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, DX or 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.
Outdoor Air Dampers with UC400-B Controller
Table 59. Outdoor air damper remains closed
Probable Cause
Explanation
Unit wiring
The wiring between the controller outputs and the outdoor air damper must be present and correct for
normal outdoor air damper operation. Refer to applicable wiring diagram.
Failed end device
Check damper actuator to ensure proper operation.
No power to the controller
If the controller does not have power, the outdoor air damper does 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 outdoor air damper operation. For detailed information about these
diagnostics, refer to Table 54, p. 134.
Normal operation
The controller opens and closes the outdoor air damper based on the controller’s occupancy mode and
fan status. Normally, the outdoor air damper is open during occupied mode when the fan is running and
closed during unoccupied mode.
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, the outdoor air damper may not work
correctly.
Warm-up and cool-down
sequence
The controller includes both a morning warm-up and cool-down sequence to keep the outdoor air damper
closed during the transition from unoccupied to occupied. This is an attempt to bring the space under
control as quickly as possible.
Requested mode off
The user can communicate a desired operating mode (such as OFF, heat, or cool) to the controller. If
OFF is communicated to the controller, the unit closes the outdoor air damper.
Table 60. Outdoor air damper remains open
Probable Cause
Explanation
Unit wiring
The wiring between the controller outputs and the outdoor air damper must be present and correct for
normal outdoor air damper operation. Refer to applicable wiring diagram.
Failed end device
Check damper actuator to ensure proper operation.
Diagnostics and Troubleshooting
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