Instruction manual

56 McQuay OM 920
Alarms
Alarms
Alarms provide the user with information about abnormal conditions that affect unit operation.
The cause of the alarm should be investigated and eliminated before the unit or any disabled
equipment in it is placed back into service.
Faults are conditions that are serious enough to shut down the unit. The alarm must be
manually cleared to allow unit operation.
Problems are conditions that result in some limitation of unit operation, but the unit is allowed
to continue to operate. Some of these alarms must be cleared manually, but others clear
automatically.
Warnings inform the user of conditions that should be addressed, but do not limit operation in
any way. The alarm condition needs to be fixed and the alarm must be manually cleared to
cause this alarm to no longer be active.
All active alarms as well as the date and time that they were detected are displayed on the
Active Alarm menu. These alarms are displayed in order of priority. Higher priority alarms are
displayed first. The last fifty alarm “events” detected as well as the date and times that they
were detected are displayed on the Alarm Log menu. An alarm “event” is either an alarm
becoming active or being cleared. A “+” symbol precedes the active alarm event and a “-
”symbol precedes the cleared alarm event. These alarms are displayed in the order that they
were detected. The alarm that was detected most recently is displayed first. Multiple
occurrences of the same alarm may appear.
Alarm Clearing
Active alarms can be cleared through the keypad/display or a BAS network. Alarms are
automatically cleared when power is cycled. Alarms are cleared only if the conditions required
to initiate the alarm do not exist. All alarms and groups of alarms can be cleared via the
network or keypad by setting the ClearAlms variable to a non-zero value as indicated in the
table below.
Note – The enumeration text is what shows up on the keypad/display not the number. The value
of this variable automatically reverts to zero when the alarms are cleared. This variable
may be set through the keypad at the end of the Active Alarm menu. It may be set via LON
using nviClearAlarms and via BACnet using the ClearAlarms object.
Warnings
Dirty Filter
If the pressure drop across the filter section in the unit exceeds the setting of the differential
pressure switch the Dirty Filter warning occurs. When the Dirty Filter warning occurs, unit
operation is not affected. The Dirty Filter warning must be manually cleared through the unit
keypad or via a network signal.
Airflow Switch
If the unit has been in the Off operating state for at least thirty minutes and the PC7 airflow
switch input to the main controller indicates airflow, the Airflow Switch warning occurs. This
normally indicates a problem with the PC7 airflow switch. When the Airflow Switch warning
occurs, unit operation is not affected. When the alarm condition is corrected, the Airflow
Switch warning must be manually cleared through the unit keypad or via a network signal.
Table 52: Alarm Clearing
Value Action
0 None
1 Clear All Faults
2 Clear All Problems
3 Clear All Warnings
4 Clear All Alarms