36 Alarm Descriptions
5.1.10 Loss of Air Flow
A differential air pressure switch is used to indicate loss of air flow in Himod 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.
5.1.11 Loss 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.
5.1.12 Low 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.
5.1.13 Low Suction Pressure
A pressure switch monitors the suction pressure at the compressor inlet. It opens when the pressure
drops below a factory preset point. Above the factory preset point, the switch is closed. If the low pres-
sure switch fails to close within five (5) minutes after the compressor is commanded to run and the
positive start kit time delay has timed out, the alarm is activated. Also, after a call for cooling has
been satisfied and the compressor turns off, if the low pressure switch does not open within 10 sec-
onds, the control will briefly energize the liquid line solenoid valve once per minute. If the low pres-
sure switch still does not open, an alarm is activated. The alarm will be displayed as an active alarm
for ninety (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.
5.1.14 Low 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.)
5.1.15 Main Fan Overload
A standard tri-block overload is provided 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.
5.1.16 Short Cycle
On compressorized systems, if the compressor has exceeded 10 cooling starts in a one hour period, or
the compressor has cycled 5 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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