Diagnostics and Troubleshooting
UNT-SVX041D-EN
81
Table 42. Diagnostics generated by UC400-B controller
Diagnostic
Probable Cause
Consequences
Diagnostic Type
Filter change required
Fan run hours exceed the time set to
indicate filter change.
• Fan
Unaffected
• Valves
Unaffected
• Electric heat
Unaffected
Informational
Condensate overflow
The drain pan is full of water.
• Fan
OFF
• Valves
Closed
• Outdoor air damper
Closed
• Electric heat
OFF
Manual
Low coil temp detection
The leaving fluid temperature may be
close to freezing.
• Fan
OFF
• Valves
Open
• Outdoor air damper
Closed
• Electric heat
OFF
Smart reset/Manual
Low airflow supply fan
failure
The fan drive belt, contactor, or motor has
failed.
• Fan
OFF
• Valves
Closed
• Outdoor air damper
Closed
• Electric heat
OFF
Manual
Space temperature
failure
(a)
Invalid or missing value for zone
temperature.
• Discharge air temperature control runs
• Unit shuts
OFF
if both space temperature and
discharge air temperature fail
Automatic
Entering water temp
failure
Invalid or missing value for zone
temperature.
• Fan
Unaffected
(enabled)
• Valves
Unaffected
• Outdoor air damper
Unaffected
• Electric heat
Unaffected
Automatic
Discharge air temp low
limit
Discharge air temperature has fallen
below the Discharge Air Temperature Low
Limit.
• Fan
OFF
• Valves
Open
• Outdoor air damper
Closed
• Electric heat
OFF
Smart reset/manual
Discharge air temp
failure
Invalid or missing value for discharge air
temperature.
• Simplified zone control algorithm runs
• Unit shuts OFF if zone temperature fails
Automatic
Outdoor air temp failure
Invalid or missing value for outdoor air
temperature.
• Fan
Unaffected
• Valved
Unaffected
• Outdoor air damper
Minimum
Position
• Electric heat
unaffected
Automatic
Humidity input failure
Invalid or missing value for relative
humidity.
• Fan
Unaffected
• Valves
Unaffected
• Outdoor air damper
Unaffected
• Electric heat
Unaffected
Automatic
CO
2
sensor failure
Invalid or missing value for CO
2
.
• Fan
Unaffected
• Valves
Unaffected
• Outdoor air damper
Unaffected
• Electric heat
Unaffected
Informational
Generic AIP failure
Invalid or missing value for generic
analog input.
• Fan
Unaffected
• Valves
Unaffected
• Outdoor air damper
Unaffected
• 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
• 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
• Electric heat
Unaffected
Automatic
(a) For detailed information about zone temperature control methods, refer to
“Zone Temperature Control,” p. 65.
Fans with UC400-B Controller
Table 43. 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
.
