BCX-SVX002A-EN
135
Table 54. Diagnostics generated by UC400-B controller (continued)
Diagnostic Probable Cause Consequences Diagnostic Type
Generic AIP failure Invalid or missing value
for generic analog input.
• Fan Unaffected
• Valves Unaffected
• Outdoor air damper Unaffected
• DX cooling/electric heat Unaffected
Informational
Local fan mode
failure
Invalid or missing fan-
speed switch (reverts to
default fan speed).
• Fan Unaffected
• Valves Unaffected
• Outdoor air damper Unaffected
• DX cooling/electric heat Unaffected
Automatic
Local setpoint failure Invalid or missing value
for zone temperature
setpoint (reverts to default
setpoint).
• Fan Unaffected
• Valves Unaffected
• Outdoor air damper Unaffected
• DX cooling/electric heat Unaffected
Automatic
(a)
For detailed information about zone temperature control methods, refer to Zone Temperature Control, p. 108.
Fans with UC400-B Controller
Table 55. Fan does not energize
Probable Cause Explanation
Unit wiring The wiring between the controller outputs and the fan relays and contacts must be present and correct for normal fan
operation. Refer to applicable wiring diagram.
Failed end device The fan motor and relay must be checked to ensure proper operation.
Normal operation The fan will turn OFF when:
• The controller receives a communicated off signal.
• The fan-speed switch is set to OFF if no communicated value is present.
• Specific diagnostics are generated.
• The default fan speed is set to OFF and the fan is operating in the Auto mode.
If the controller is in unoccupied mode, the fan cycles between OFF and the highest fan speed.
No power to the controller If the controller does not have power, the unit fan does not operate. For the controller to operate normally, it must have 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 fan operation. For detailed information about these diagnostics, refer to Table 54, p. 134.
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 fans may not work correctly.
Random start observed After power-up, the controller always observes a random start from 5 to 30 seconds. The controller remains OFF until the
random start time expires.
Cycling fan operation/
continuous
The controller continuously operates the fan when in the occupied, occupied standby, or occupied bypass mode. When
the controller is in the unoccupied mode, the fan is cycled between high speed and OFF with capacity.
Unoccupied operation Even if the controller is configured for continuous fan operation, the fan normally cycles with capacity during unoccupied
mode. While unoccupied, the fan cycles ON or OFF with heating/cooling to provide varying amounts of heating or cooling
to the space.
Fan mode off If a local fan mode switch determines the fan operation, the OFF position controls the fan to off.
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 controls the fan to off. There is no heating or cooling.
Diagnostics and Troubleshooting
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