PHASE LOSS
If the digital input for the phase loss indicator is on and it remains on for two seconds, the MHRC will be
locked out and a “PHASE LOSS” alarm generated. This fault requires a manual reset via the LCD/Keypad or
MCS-CONNECT.
HIGH CONDENSATION
If the digital input for the high condensation indicator is on and it remains on for the time specifi ed in the
safety time of that setpoint, #58, a “HI SUMP LVL” alarm is generated. This alarm will identify which indicator
is on. No change to system status will be made.
21.5. MHRC Compressor Safeties
21.5.1 Introduction
The MHRC MAGNUM algorithm incorporates a number of safety checks to ensure that the various compo-
nents that make up the MHRC package are not damaged. These types of safeties are based upon setpoints.
When a safety trip occurs the compressor’s state goes to “SAFETY TRIPPED”. The compressor state will
remain as “SAFETY TRIPPED” for ten minutes before the compressor’s state is set to “CMP IS OFF” state. If
a second safety trips occurs within two hours of the fi rst trip, the compressor state becomes “CMP LOCKED
OUT”. In this matter the MHRC MAGNUM attempts to take corrective action before any internal safeties of the
compressors are activated or the MHRC unit is damaged.
21.5.2 Compressor safeties
For a safety to be interrogated, both the associated sensor input and the lockout setpoint must be active. If
a safety trips, the alarm name will consist of the setpoint name plus a number indicating which compressor
tripped.
The following are a list of safeties that are incorporated in the MHRC control for scroll compressors. These
safeties are checked every second. Each compressor is tested individually. If a safety condition exists, action
will be taken on that compressor only, other compressor will continue to function normally.
LOW SUCTION PRESSURE
If the suction pressure drops below the value of the setpoint #45 “LOW SUCTION” and it remains there for the
time specifi ed in the safety time of that setpoint, the compressor’s safety will trip and a : LOW SUCTION #?”
alarm will be generated.
For the fi rst 5 minutes after a compressor start, the safety time is extended by 2 minutes. This enables the
setpoint safety time to be set much tighter for normal operation.
UNSAFE SUCTION PRESSURE
Similar to the low suction pressure safety except this setpoint is set up with a lower value and a very short
safety time. If the suction pressure drops below the value of the setpoint #46 “UNSAFE SUCT” and it remains
there for the time specifi ed in the safety time of that setpoint, the compressor is locked out (this safety is not
give two trips before locking out) and an “UNSAFE SUCT #?” alarm generated.
For the fi rst 5 minutes after a compressor start, the safety time is extended by 2 times the normal safety time.
This enables the setpoint safety time to be set much tighter for normal operation.
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