BAS-SVX48H-EN
57
Operational Causes and Diagnostics
Table 12. Diagnostic Causes and Diagnostics
Probable Cause
Diagnostic
Fan Not Energizing
Unit Wiring
The wiring between the UC400 Controller outputs, fan relays, and contacts must be present and
correct for normal fan operation.
Failed End Device
The fan motor and relay must be checked to ensure proper operation.
Normal Operation
The fan turns OFF when:
• The UC400 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 UC400 Controller is in unoccupied mode, the fan cycles between OFF and the highest fan
speed.
No power to the
Controller
If the UC400 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.
Unit Configuration
The UC400 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 UC400 Controller always observes a random start from 5 to 30 seconds. The
unit remains OFF until the random start time expires.
Cycling Fan Operation/
Continuous
The UC400 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 UC400 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 controller controls the fan to off. There is
no heating or cooling.
Isolation Valves Remain Closed
Unit Wiring
The wiring between the UC400 Controller outputs and the valve(s) must be present and correct
for normal valve operation. Refer to applicable wiring diagram.
Failed End Device
The valves must be checked to ensure proper operation.
No power to the
Controller
If the UC400 Controller does not have power, the unit valve(s) will not operate. For the unit 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 valve operation. For detailed information about these diagnostics, refer
to Table 13, p. 46.
Normal Operation The UC400 Controller opens and closes the valves to meet the unit capacity requirements.
Unit Configuration
The UC400 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 valves may not
work correctly.
Random Start Observed
After power-up, the UC400 Controller always observes a random start from 5 to 30 seconds. The
controller remains OFF until the random start time expires.
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