Diagnostics and Troubleshooting
82
UNT-SVX041D-EN
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 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.
Fans with UC400-B Controller
Table 43. Fan does not energize (continued)
Probable Cause
Explanation
Valves with UC400-B Controller
Table 44. Valves remain closed
Probable Cause
Explanation
Unit wiring
The wiring between the 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 controller does not have power, the unit valve(s) will 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 valve operation. For detailed information about these diagnostics, refer to
Normal operation
The controller opens and closes the valves 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, the valves 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.
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.
Entering water temperature
sampling logic
The controller includes entering water temperature sampling logic, which 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 or normally closed
as dictated by the application. For modulating valves, ensure the stroke time is set correctly.
Table 45. Valves remain open
Probable Cause
Explanation
Unit wiring
The wiring between the 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 controller opens and closes the valves to meet the unit capacity requirements.
Diagnostic present
Several diagnostics affect valve operation. For detailed information about these diagnostics, refer to
.
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 valves may not work correctly.
Entering water temperature
sampling logic
The controller includes entering water temperature sampling logic, which 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. For modulating valves, ensure the stroke time is set correctly.
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 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
.
