Page 39: 6 high temperature, 8 humidifier problem, Infrared humidifiers, Steam generating (canister) humidifiers, High head pressure, High humidity, High humidity and low humidity (simultaneously)
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6.1.3 High Head Pressure
Compressor high head is monitored with a pressure switch. One SPDT pressure switch is used for the
compressor in the unit. If head pressure exceeds 360 PSIG, the switch opens the compressor contactor
and sends an input signal to the control. On a self-contained system, the head pressure switch located
at the compressor requires a manual reset and the alarm condition to be acknowledged on the front
display panel. On a split system, the high head pressure condition is acknowledged by pressing the
alarm silence button that will clear the alarm if the high head pressure condition no longer exists. On
a split system, if the compressor is Off for 1 hour, the control goes into a special “cold start mode.” In
the cold start mode on a call for cooling or dehumidification, the Liquid Line Solenoid Valve (LLSV) is
energized. If the high pressure switch does NOT trip within 10 seconds, the control returns to normal
operation of monitoring the high head pressure switch for three occurrences in a 12-hour period. It is
a rolling timer; after the third high head alarm occurs and is acknowledged by the user, it will lock Off
the compressor. If while in the cold start mode, the high head pressure switch DOES trip within 10
seconds of the activation of the LLSV, the control does not annunciate the alarm. The control will turn
Off the LLSV and delay 10 seconds. The control will permit this occurrence two more times or a total
Liebert Icom Manual
of three times. If on the fourth try the high head pressure switch trips within 10 seconds, the control
will annunciate the alarm, turn Off the LLSV, wait for the user to acknowledge the alarm and hold
the compressor Off for three minutes, which is the normal short cycle control. On the third occur-
rence, the control will lock the compressor Off until the control power is reset.
On air cooled systems, check for power shut Off to the condenser, condenser fans not working, defec-
tive head pressure control valves, closed service valves, dirty condenser coils, and crimped lines. Also,
make sure that when the compressor contactor is energized, the side switch on the contactor closes to
energize the control circuit on the air cooled condenser.
On water/glycol/GLYCOOL systems, check water regulating valves. Verify water/glycol flow (are
pumps operating and service valves open?). Is water tower or drycooler operating? Is the coolant tem-
perature entering the condenser at or below design conditions? Is relay R5 operating during cooling to
turn On the drycooler?
6.1.4 High Humidity
The return air humidity has increased to the High Humidity Alarm setpoint. Is the unit setup for
dehumidification (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 cooling system is working properly (the cooling system dehumidifies).
6.1.5 High Humidity and Low Humidity (Simultaneously)
If these two alarms are displayed at the same time, the humidity input signal is lost. Dashes will be
displayed for the humidity reading. The control system will deactivate humidification and dehumidi-
fication. Check for a disconnected cable or a failed sensor.
6.1.6 High Temperature
If the return air temperature has increased to the High Temperature Alarm setpoint, check for proper
setpoints. Is the room load more than the unit can handle (is the unit capacity too small)? Run diag-
Liebert Icom Installer User Guide
nostics to make sure all cooling components are operating (compressor and/or valves).
6.1.7 High Temperature and Low Temperature (Simultaneously)
If these two alarms are displayed at the same time, the temperature input signal is lost (or the
humidity is out of sensor range: 15 to 85% RH). Dashes will be displayed for the temperature reading.
The control system will initiate 100% cooling. Check for a disconnected cable or a failed sensor.
6.1.8 Humidifier Problem
This alarm is activated by the high-water float switch in the humidifier pan assembly. The high-
water float switch is normally closed and opens upon alarm condition. Check for drain clog and, if
present, clean drain. Check for float switch stuck high; replace the switch as necessary. Check for
proper operation of the humidifier water makeup valve.
Steam Generating (Canister) Humidifiers
This alarm is activated by a signal from the humidifier control indicating that the canister needs to be