Emerson 3000/ITR manual 6.1.9Loss of Air Flow, 6.1.10Loss of Power, 6.1.11Low Humidity

Alarm Descriptions

6.1.9Loss of Air Flow

A differential air pressure switch is used to indicate loss of air flow in Liebert Challenger 3000/Lie- bert Challenger ITR units.

Check for blockage of unit air outlet or inlet. Check blower motor fuses and overload reset. Check for broken belts. Make sure blower wheels are tight to shaft. Run diagnostics to see if the fan contactor is working properly.

6.1.10Loss of Power

If the unit has lost power, or the disconnect switch was turned Off before the unit On switch was pressed (to turn the unit Off), this local alarm will occur when power is restored to the unit. A Liebert remote monitoring unit (optional) will immediately indicate loss of power.

6.1.11Low Humidity

If the return air humidity has decreased to the Low Humidity Alarm setpoint, check to make sure that the unit is setup for humidification (check DIP switch). Check for proper setpoints. Does the room have a vapor barrier to seal it from outdoor humidity? Are doors or windows open to outside air? Run diagnostics to make sure the humidifier system is working properly.

6.1.12Low Suction Pressure

A pressure switch monitors the suction pressure at the compressor inlet to monitor whether pressure has dropped below a factory preset point while the compressor is in cooling operation. When pressure drops below a factory preset point, the switch opens. After the positive start kit time delay, and the switch stays open for five minutes, the alarm is activated. The alarm stays active for 90 minutes.

Look for conditions that would cause loss of refrigerant. Check for piping problems such as leaks or crimped lines. Check for inoperative components such as liquid line solenoid valve, low pressure switch, expansion valve, and head pressure control valve. Check for closed service valves in the liquid line or at the condenser or receiver.

6.1.13Low Temperature

If the return air temperature has decreased to the Low Temperature Alarm setpoint, check for proper setpoints. Run diagnostics to make sure all heating components are operating (contactors and reheats). Are reheats drawing the proper current? (See nameplate for amp rating.)

6.1.14Main Fan Overload

An optional tri-block overload is required for this alarm, and may or may not replace internal motor overload, depending on your model. The overload device is located next to the main fan contactor in the line voltage section. The alarm is activated when the overload is tripped.

6.1.15Short Cycle

On compressorized systems, if the compressor has exceeded 10 cooling starts in one hour or if the compressor has cycled five times in 10 minutes on the low pressure switch during non-cooling, the Short Cycle alarm will occur. This can be caused by low refrigerant level (but not low enough to acti- vate Low Suction Pressure alarm) or room cooling load is small compared to capacity of the unit.

Check for leaks, crimped lines, and defective components. If room load is low, increase sensitivity to reduce cycling (proportional control). On GLYCOOL units, dirty filters can cause the coil freeze stats to cycle the compressor.

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