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SCXG-SVX01B-EN 115
Diagnostic
Troubleshooting Diagnostics
UCM’s Reaction: The system mode
reverts to the default (HI set) system
mode.
Reset Required: (INFO) An automatic
reset occurs after the mode input returns
to its allowable range for 10 seconds.
N
NSB Panel Zone Temperature Sensor
Failure
Problem: The NSB panel's zone temp
sensor input is out of range. (This input is
at the NSB panel, not on the unit itself).
Check: If have an external sensor
connected to the NSB panel zone sensor
input, then the internal NSB panel zone
sensor should be disabled. Verify sensor
resistance. If in valid range, check wiring
between the sensor and NSB panel.
NSB Panel Comm Failure
Problem: The RTM has lost
communications with the night setback
panel (programmable zone sensor).
Check: Field/unit wiring between RTM
and NSB Panel.
Reason for Diagnostic: The RTM has lost
communication with the NSB panel.
UCM’s Reaction: The unit reverts to the
next lower priority mode switching
source (typically the HI default mode). If
the NSB panel zone sensor is the
designated sensor source for any
functions, those functions are disabled.
Reset Required: (PAR) An automatic reset
occurs after communication has been
restored.
O
O/A Humidity Sensor Failure
Problem: The outside air humidity sensor
data is out of range.
Check: Check field/unit wiring between
the sensor and RTM.
Reason for Diagnostic: The unit is reading
a signal that is out of range for the outside
air humidity sensor (humidity < 5% or
humidity > 100%).
UCM’s Reaction: The economizer enable
r.e enthalpy function reverts to dry-bulb
temperature changeover (“Level 1”)
control.
Reset Required: (PAR) An automatic reset
occurs after the OA humidity input
returns to its allowable range for 10
seconds.
O/A Temp. Sensor Failure
Problem: The outside air temperature
sensor input is out of range.
Check: Sensor resistance should be
between 830 ohms (200 F)and 345.7
Kohms (-40 F). If so, check field/unit wiring
between sensor and RTM.
Reason for Diagnostic: The unit is reading
a signal that is out of range for the outside
air temperature input on the RTM (temp.
< -55 F or temp > 209 F).
UCM’s Reaction: These unit functions
occur:
• low ambient compressor lockout
disables
• O/A damper drives to minimum position
• on VAV units with S/A temp. reset type
selected as O/A temp. reset, the reset
type reverts to “none” for the duration
of the failure
Reset Required: (PAR) an automatic reset
occurs after the O/A temperature input
returns to its allowable range. To prevent
rapid cycling of the diagnostic, there is a
10 second delay before the automatic
reset.
Occupied Zone Heat Setpoint Failure
Problem: The occupied zone heat setpoint
input is out of range.
Reason for Diagnostic: The input
designated as occupied zone heating
setpoint source is out of range for the
outside air temperature input on the RTM
(temp. < 45 F or temp > 94 F).
UCM’s Reaction: The active occupied
zone heating setpoint reverts to the
default value.
Reset Required: (PAR) an automatic reset
occurs after the occupied zone heating
setpoint input returns to its allowable
range for 10 continuous seconds, or after
a different occupied zone heating setpoint
selection source is user-defined.
R
Return Air Humidity Sensor Failure
Problem: On units with both airside
economizer and comparative enthalpy
installed, the return air humidity sensor
input is out of range.
Check: Check field/unit wiring between
the sensor and ECEM.
Reason for Diagnostic: The unit is reading
a signal that is out of range for the return
air humidity sensor (humidity < 5% or
humidity > 100%).
UCM’s Reaction: The economizer enable
r.e. enthalpy function reverts to reference
enthalpy changeover (“Level 2”) control.
Reset Required: (PMR) An automatic
reset occurs after the RA humidity input
returns to its allowable range
continuously for 10 seconds.
Return Air Temp Sensor Failure
Problem: On units with the comparative
enthalpy option, the return air
temperature sensor input is out of range.
Check: Sensor resistance should be
between 830 ohms (200 F) and
345.7Kohms (-40 F). If so, check field/unit
wiring between the sensor and ECEM.
Reason for Diagnostic: The unit is reading
a signal that is out of range for the return
air humidity sensor (temp < -55 F or
temp > 209 F).
UCM’s Reaction: The economizer enable
r.e. enthalpy function reverts to reference
enthalpy changeover (“Level 2”) control.
Reset Required: (PAR) An automatic reset
occurs after the RA temp input returns to