Emerson 3000/ITR Manuale Utente

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.

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.

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.

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.

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.)

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.

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.