58
BAS-SVX48H-EN
Table 12. Diagnostic Causes and Diagnostics (continued)
Probable Cause
Diagnostic
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 UC400 Unit, it controls the fan to off. There is no heating
or cooling.
Entering Water
Temperature Sampling
Logic
The UC400 Controller includes entering water temperature sampling logic It is automatically
initiated during 2-pipe and 4-pipe changeover if the entering water temperature is either too cool
or too hot for the desired heating or cooling.
Valve Configuration
Ensure the valves are correctly configured, using the Tracer TU service tool, as normally open
(NO) or normally closed (NC) as dictated by the application.
Isolation Valves Remain Open
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 operations.
Normal Operation The UC400 Controller opens and closes the valves to meet the unit capacity requirements.
Diagnostic Present Several diagnostics affect valve 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 valves may not
work correctly.
Entering Water
Temperature Sampling
Logic
The UC400 Controller includes entering water temperature sampling logic. It is automatically
initiated during 2-pipe and 4-pipe changeover if the entering water temperature is either too cool
or too hot for the desired heating or cooling.
Valve Configuration
Ensure the valves are correctly configured, using the Tracer TU service tool, as normally open
(NO) or normally closed (NC) as dictated by the application.
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 UC400 Controller opens the water valves (100%) to prevent
coil freezing. This includes unoccupied mode when there is no call for capacity or any other time
the fan is OFF.
DX or Electric Heat Outputs Do Not Energize
Unit Wiring
The wiring between the UC400 Controller outputs and the end devices must be present and
correct for normal operation.
Failed End Device
Check the UC400 Controller contactors or the electric heat element, including any auxiliary safety
interlocks, to ensure proper operation.
No Power to the
Controller
If the UC400 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.
Normal Operation
The UC400 Controller controls compressor or electric heat outputs as needed 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, 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 UC400 Controller, the controller 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 UC400 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 Damper Remains Closed
Unit Wiring
The wiring between the UC400 Controller outputs and the outdoor air damper must be present
and correct for normal outdoor air damper operation. Refer to applicable wiring diagram.
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