Liebert 50 & 60Hz User Manual

The microprocessor control system will audibly and visually signal all ENABLED Alarms (including 

two (2) custom alarms). These special alarms can be chosen from the optional alarm list and/or can 

have their own fully custom text. The custom alarm inputs are contact closures wired from terminal 

24 through a normally open contact to either 50 (alarm 1), 51 (alarm 2), or 56 (alarm 3). The alarms 

can be enabled/disabled (refer to 3.0 - Microprocessor Control) and a time delay of 0-255 seconds 

can be set. The alarms can also be programmed to either sound the alarm & activate the common 

alarm relay OR to sound the alarm only.
When a new alarm occurs, it is displayed on the screen and the audible alarm is activated. (If commu-

nicating with a Liebert Site Product, the alarm is also transmitted). The message “PRESS ALARM 

SILENCE” will prompt the operator to silence the alarm. After the alarm is silenced, the display will 

return to the Normal Status Display. Alarms can be reviewed by selecting the “ACTIVE ALARMS” 

feature. The alarms can also be silenced through communications with a Liebert Site Products Unit. 
Many alarms will reset automatically when the alarm condition is no longer present and only after it 

has been acknowledged by being “Silenced.” The exceptions are:
1. Software alarms, i.e., Loss of Power and Short Cycle alarms will reset automatically 30 seconds 

and 90 minutes respectively, after being silenced or acknowledged; and

2. Specific alarms monitoring overload or high pressure switches may require a manual reset 

depending upon the model.

The following list provides a definition and troubleshooting suggestions for each type of alarm. Refer 

to 8.0 - Troubleshooting for additional details. If you need further assistance, contact your Liebert 

supplier. THE CUSTOMER MUST SPECIFY ALARM(S) AT THE TIME OF ORDER. OTHER 

DEVICES AND WIRING MAY BE REQUIRED AT THE FACTORY FOR SOME OF THE ALARMS.

Custom alarm(s) messages are programmed at the LCD display. The message displayed may be 

included in a list of provided alarms or it may be customized text (for up to three alarms). IF CUS-

TOMIZED TEXT IS USED, MAINTENANCE PERSONNEL SHOULD BE INFORMED OF THE 

ALARM FUNCTION AND THE REQUIRED ACTION.

Compressor head pressure is monitored with a pressure switch. (One SPDT pressure switch is used). 

If head pressure exceeds 360 psig, the switch turns off the compressor contactor and sends an input 

signal to the control. The condition is acknowledged by pressing the alarm silence button on the wall 

box, which will clear if the head pressure is alleviated. If the head pressure alarm has activated three 

times, the alarm will lock until the unit is serviced. After the head-pressure problem is fixed, reset the 

control by disconnecting power to the evaporator unit.

Check for power shut off to the condenser, condenser fans not working, defective head pressure con-

trol valves, dirty condenser coils or crimped lines. 

Check water regulating valves. Verify water/glycol flow (i.e., pumps operating and service valves 

open). Is water tower or drycooler operating? Is the coolant temperature entering the condenser at or 

below design conditions? Is AUX relay (terminals 70 & 71) operating during cooling to turn on the 

drycooler?