IOMM AGR AGR 055A through 100A 71
Pumpdown Control
The AGR units have a limited recycling pump down. Certain alarm conditions will not permit
chiller pumpdown. These alarm conditions are:
• High Condenser Pressure
• Bad Evap Pressure Sensor
• Phase Voltage Monitor (optional)
• Volts Ratio Protect
• Mechanical High Pressure Switch
• Compressor Motor Protect
• Ground Fault (optional)
Safety Systems
MicroTech continuously performs self diagnostic checks, monitoring all system temperatures,
pressures and safeties, and will automatically shut down a refrigerant circuit or the entire unit
should a fault occur. The cause of the shutdown, time and date of occurrence and conditions at the
same time of alarm will be retained in memory and can be displayed for the operator to review.
The MicroTech controller has several safety systems to safeguard against potential damage of the
chiller equipment. There are alarm and pre-alarm conditions. Alarm conditions cause the
compressors to shut off and/or lockout. Pre-alarm conditions cause the unit to stage down in
capacity in an attempt to avoid an alarm condition. For alarm conditions, the red “Alarm Status”
light on the control panel will be solid. For all pre-alarm conditions, the light will pulse at the rate
of 0.5 seconds on, 4 seconds off. When an alarm of pre-alarm condition exists, the MicroTech
display automatically switches to the alarm menu to alert the user of the condition.
The MicroTech controller alarms can either be of the manual reset type or the auto reset type.
Critical alarm conditions such as High Condenser Pressure, Refrigerant Freeze Protection, and Low
Evaporator Pressure which protect against equipment damage are manual reset, which means they
lockout compressor operation and must be cleared at the MicroTech keypad before operation can
resume. Auto-clearing alarm conditions cause the compressors to shut off on the affected circuit
until the condition is corrected. When the condition is corrected, the chiller will resume normal
operation on that circuit, provided the anti-cycle timers have cleared and sufficient load exists. All
pre-alarm conditions are auto-clearing. After the controller stages down the unit on an alarm
condition and the potential alarm condition has been avoided, the alarm will clear y itself and the
unit will resume normal operation. If the alarm condition is not avoided, the alarm will be logged
on the MicroTech display, causing lockout of compressors. Thus, the alarm must be manually
cleared.
When a McQuay Chiller with a MicroTech controller is used with the McQuay RMS (Remote
Monitoring and Sequencing) Panel, the user must note that alarm nomenclature varies. The RMS
has three possible categories of alarms: faults, problems, and warnings. The chiller alarm
condition corresponds with the RMS “fault” condition. Thus, there are system and circuit faults.
Chiller pre-alarm conditions correspond to the RMS “problem” designation. Reciprocating chillers
do not have warning alarms.
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