Installation and Maintenance Manual

Diagnostics
UNT-SVX07D-EN 125
Table 58. DX or electric heat does not energize (UC400)
Probable
Cause Explanation
Unit wiring The wiring between the controller outputs and the end
devices must be present and correct for normal operation.
Refer to applicable wiring diagram.
Failed end
device
Check the control contactors or the electric heat element,
including any auxiliary safety interlocks, to ensure proper
operation.
No power to
the controller
If the 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.
For detailed information about these diagnostics, refer to
Table 44, p. 116.
Normal
operation
The controller controls compressor or electric heat outputs
as needed 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, 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 controller, the unit 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 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.
Table 59. Outdoor air damper remains closed (UC400)
Probable
Cause Explanation
Unit wiring The wiring between the controller outputs and the outdoor
air damper must be present and correct for normal outdoor
air damper operation. Refer to applicable wiring diagram.
Failed end
device
Check damper actuator to ensure proper operation.
No power to
the controller
If the controller does not have power, the outdoor air
damper does 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 outdoor air damper operation.
For detailed information about these diagnostics, refer to
Table 44, p. 116.
Normal
operation
The controller opens and closes the outdoor air damper
based on the controller’s occupancy mode and fan status.
Normally, the outdoor air damper is open during occupied
mode when the fan is running and closed during
unoccupied mode.
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
outdoor air damper may not work correctly.
Warm-up and
cool-down
sequence
The controller includes both a morning warm-up and cool-
down sequence to keep the outdoor air damper closed
during the transition from unoccupied to occupied. This is
an attempt to bring the space under control as quickly as
possible.
Requested
mode off
The user can communicate a desired operating mode (such
as OFF, heat, or cool) to the controller. If OFF is
communicated to the controller, the unit closes the outdoor
air damper.
Table 60. Outdoor air damper remains open
Probable
Cause Explanation
Unit wiring The wiring between the controller outputs and the outdoor
air damper must be present and correct for normal outdoor
air damper operation. Refer to applicable wiring diagram.
Failed end
device
Check damper actuator to ensure proper operation.
Normal
operation
The controller opens and closes the outdoor air damper
based on the controller occupancy mode and fan status.
Normally, the outdoor air damper is open during occupied
mode when the fan is running and closed during
unoccupied mode. (Refer to the section, “Modulating
Outdoor/Return Air Damper (UC400),” p. 102.)
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
outdoor air damper may not work correctly.
UNT-SVX07_-EN.book Page 125 Friday, April 27, 2012 9:40 AM