FORM 201.10-NM4
83
YORK INTERNATIONAL
LOW COMPRESSOR MOTOR CURRENT CUTOUT /
MOTOR PROTECTOR (HI MOTOR WINDING TEMP
CUTOUT)/MECHANICAL HIGH PRESSURE CUTOUT
The Low Motor Current Safety prevents a compressor
motor running with less current than would normally be
expected. This may result from a loss of refrigerant,
contactor or power problems as well as from a com-
pressor that is not pumping due to a mechanical mal-
function. Motor current is monitored using 3 Current
Transformers (C.T.s) per motor, one on each phase.
Average motor current is monitored after five seconds
(Across-The-Line Starters) or twenty seconds (Wye-
Delta Starters) of compressor operation. From this time
the system will be shut down if average motor current
is less than 5% of FLA for ambient temperatures < 25°F,
10% of FLA for ambient = 26 45°F, or 15% FLA for
ambient > 45°F, for more than three seconds.
Compressor motor protection modules, external motor
overloads and mechanical high pressure cutouts are fit-
ted to each system. All these devices stop the compres-
sor by removing power from its motor contactor coils.
This causes the C.T.s to obviously sense a zero current
draw by the compressor motor and causes a Low Motor
Current Fault to be displayed. These devices operate as
follows:
The Motor Protection Module protects against exces-
sive motor winding temperature by monitoring 3 or 6
sensors built into the motor windings. If the tempera-
ture becomes excessive the module will cause power
to be removed from the compressor contactors, shut-
ting down the compressor. Auto restart will not occur
since manual reset is required. A fault lockout will auto-
matically occur after the micro attempts two more starts
with the MP contacts open. Manual reset is accom-
plished by removing 115VAC control power from the
micro panel after the motor sensors have sufficient time
to cool.
The External Motor Overload is responsive to motor
current. When the overload relay senses single phase
operation, locked rotor current in excess of 10 seconds,
or sustained current overloads in excess of 140% of
RLA, it will trip. This causes power to be removed from
the compressor contactors and shuts down the
compressor.
Auto-restart will not be permitted as a manual reset of
the device is required to restart the compressor. After
the first fault, the micro will try two more restarts, but
with the External Motor Overload Relay tripped, no re-
start can occur. The micro will then lock out the system.
In addition to manually resetting the External Motor
Overload Relay, the fault will also require reset by turn-
ing the appropriate system switch OFF, then ON.
The Overload Relay setting should never be altered. If
for some reason the Overload Relay is replaced, the
following procedure is used for setup:
A/L Start:
Dial Setting = (1.1 x RLA) / 350
WYE-Delta Start:
Dial Setting = (0.64 x RLA) / 350
The Mechanical HP (High Pressure) Cut-out will also
cause the low current safety to activate. If discharge
pressure exceeds 405 PSIG (HP cut-out), the cut-out
will open. When the cut-out opens, 115VAC power will
be removed from the Motor Protector Module. When
power is removed from the module, its MP contacts will
open, breaking the 115VAC fed to the 1CR (SYS 1) or
2CR (SYS 2) control relay. When a control relay is de-
energized, power is removed from the compressor con-
tactors which shuts the compressor off. When the mo-
tor contactor de-energizes, motor current falls to zero.
The low motor current is sensed by the microprocessor
and the system is shut down.
Auto-restart will be permitted after shutdown, when dis-
charge pressure drops below 330 PSIG and the HP
contacts close. A fault lock-out will result if safety thresh-
olds are exceeded three times in a 90 minute period.
2.6 PRINTOUT ON FAULT SHUTDOWN
If an optional printer is installed, the contents of History
Buffer #1 will be sent to the printer any time a fault shut-
down occurs. This will allow record keeping of individual
faults, even if they do not cause a lockout of the system.
This information may be useful in identifying developing
problems and troubleshooting. See also Section 4.7.
The No Run Permissive fault messages will not be
stored in the History Buffer and will not cause an auto
printout.
NOTE: Due to extreme operating conditions or systems
where control deficiencies are present, occa-
sional faults may occur with the automatic print-
out. This is not a cause for concern.
S Y S
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L O W
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S Y S
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L O W
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