Instruction manual

McQuay OM 920 61
Alarms
Control Temperature Fault
If the temperature sensor (ZNT1, RAT, OAT, MAT) selected as the Control Temperature
source is not reliable for longer than the Sensor Alarm Delay (Default= 30 seconds), a Control
Temperature Fault occurs. When the Control Temperature Fault occurs, the unit is shut down.
It remains shut down until the Control Temperature Fault is manually cleared through the unit
keypad or via a network signal.
Emergency Stop Fault
An Emergency Stop Fault will occur if either of the following conditions is true:
• Emergency Stop Input in the Alarm (Open) condition
• The Net Emrg Ovrd input is set to Off via a network signal or the keypad/display
Freeze Fault
When a unit is equipped with a waterside economizer, chilled water, hot water, or steam coil,
the Freeze Fault occurs when the optional freezestat contacts open as a result of detecting an
abnormally low water or steam coil temperature while the fans are running.
When the Freeze fault occurs, the controller shuts down the fans, opens the chilled water,
economizer, and heating valves and set a 10-minute timer. If the unit is equipped with a
waterside economizer, the pump output is also turned on. When the 10-minute timer expires,
the controller checks the freezestat input again. If the freezestat contacts are closed the pump
output is de-energized and the valves close. If the freezestat contacts are still open the pump
output remains energized, the valves remain open, and the 10-minute timer resets. This
continues until the fault is manually cleared through the keypad or via a network signal.
Note – Water valves remain open and Pump output remains on for 10 minutes after alarm
conditions disappear.