VCB-X Controller Field Technical Guide
SEQUENCE OF OPERATIONS
75
Alarms
Sensor Failure Alarms
Supply Air Temperature Sensor Failure Alarm
The Supply Air Temperature Sensor Failure Alarm is generated
when the controller detects an open or short circuit on the Supply
Air Temperature Sensor input. Once the alarm is generated, the unit
will be completely shut down. If a sensor is properly detected after
the unit has alarmed, the alarm will be cleared and the unit will
restart operations.
Space Temperature Sensor Failure Alarm
If the Space Sensor is con
fi
gured as the Controlling Sensor (Mode
Enable Sensor) or as the Reset Sensor, and if the controller detects
an open or short circuit on the Space Sensor input, then a Space
Temperature Sensor Failure Alarm is generated. If the Space Sensor
is con
fi
gured as the Controlling Sensor and the Failure Alarm is
generated, the unit will shut down. If the Space Sensor is only
con
fi
gured as a Reset Sensor and the Failure Alarm is generated,
the Space Temperature will default to a value half way between
the Heating and Cooling Mode Enable Setpoints, and the unit will
continue to run.
Outdoor Air Temperature Sensor Failure Alarm
The Outdoor Air Temperature Sensor Failure Alarm is generated
when the controller detects an open or short circuit on the Outdoor
Air Temperature Sensor input. When this occurs, the Outdoor Air
reading will be arti
fi
cially set to the half point between the Cooling
and Heating Lockout Setpoints. This will allow the cooling and the
heating to continue operating.
CO
2
Sensor Failure Alarm
This alarm is generated if the controller is con
fi
gured to have a
CO
2
sensor, but does not detect it. IAQ Mode is disabled when this
occurs. If a sensor is properly detected after the unit has alarmed,
the alarm will be cleared and the unit will be return to CO
2
control
Compressor Discharge Sensor Failure Alarm
This alarm is generated if the unit is con
fi
gured to have a digital scroll
compressor, but the Digital Compressor Discharge Temperature
Sensor is not detected or if shorted.
High
Supply
Air
Temperature
Cutoff
Low
Supply
Air
Temperature
Cutoff
High
Control
Temp
Low
Control
Temp
Digital
Compressor
Cutoff
Digital
Compressor
Lockout
High
Head
Pressure
WSHP Proof of Flow Failure
Low
Suction
Pressure
Unsafe
Suction
Pressure
WSHP
Low
Water
Temperature
Suction Pressure Sensor Failure Alarm
If the controller detects the Suction Pressure Sensor is missing,
this alarm is generated and the unit will shut down. If the sensor is
properly detected after the unit has alarmed, the alarm will be cleared
and the unit will restart.
Airfl ow Alarms
Outdoor Air
fl
ow Sensor Alarm
Supply Air
fl
ow Sensor Alarm
Return Air
fl
ow Sensor Alarm
Exhaust Air
fl
ow Sensor Alarm
If the controller is con
fi
gured to have any of the above air
fl
ow
sensors, but the controller does not detect that the sensor is connected,
then the applicable alarm will occur. If the sensor is properly detected
after the unit has alarmed, the alarm will be cleared.
Missing Expansion Module Alarm
Main Expansion Missing
Reheat Board Missing
ModGas Board Missing
12 Relay Board Missing
If the controller is con
fi
gured to have any of the above Expansion
Boards (Modules), but the controller does not detect that board, then
the applicable alarm will occur. If the board is properly detected
after the unit has alarmed, the alarm will be cleared.
Mechanical Failure Alarms
Mechanical Cooling Failure
The Mechanical Cooling Failure Alarm is generated if the Supply
Air Temperature fails to drop 5 degrees (within a user-adjustable
time period) from the temperature the supply air was at when the
cooling was activated. The alarm will be cleared when the Supply
Air Temperature drops the 5 degrees and sets the failure timer back
to zero. This alarm does not apply for Modulating Cooling.
Mechanical Heating Failure
The Mechanical Heating Failure Alarm is generated if the Supply
Air Temperature fails to rise 5 degrees (within a user-adjustable
time period) from the temperature the supply air was at when the
heating was activated. The alarm will be cleared when the Supply
Air Temperature rises the 5 degrees and sets the failure timer back
to zero. This alarm does not apply for Modulating Heating.
