York YCAL0019 Installation Operation & Maintenance Download

Page: 131 / 200

FORM 150.67-NM2 (209)

131

JOHNSON CONTROLS

The Suction Pressure Cutout is a software cutout that
helps protect the chiller from an evaporator freeze-up
should the system attempt to run with a low refrigerant
charge or a restriction in the refrigerant circuit.

Repeated starts after resetting a low
suction pressure fault will cause evapo-
rator freeze-up. Whenever a system
locks out on this safety or any safety,
immediate steps should be taken to
identify the cause.

At system start, the cutout is set to 10% of programmed
value. During the next 3 minutes the cutout point is
ramped up to the programmed cutout point. If at any time
during this 3 minutes the suction pressure falls below the
ramped cutout point, the system will stop.

This cutout is

completely ignored for the fi rst 30 seconds of system run
time to avoid nuisance shutdowns, especially on units
that utilize a low pressure switch in place of the suction
pressure transducer.

After the

rst 3 minutes, if the suction pressure falls

below the programmed cutout setting, a “transient
protection routine” is activated. This sets the cutout at
10% of the programmed value and ramps up the cutout
over the next 30 seconds. If at any time during this 30
seconds the suction pressure falls below the ramped
cutout, the system will stop.

The Motor Protector/Mechanical High Pressure Cutout
protect the compressor motor from overheating or the
system from experiencing dangerously high discharge
pressure.

This fault condition is present when CR1 (SYS 1) or
CR2 (SYS 2) relays de-energize due to the HP switch or
motor protector opening. This causes the respective CR
contacts to open causing 0VDC to be read on the inputs
to the microboard. The fault condition is cleared when a
30VDC signal is restored to the input.

S Y S 1 H I G H D S C H P R E S

S Y S 2 H I G H D S C H P R E S

S Y S 1 L O W S U C T P R E S S

S Y S 2 L O W S U C T P R E S S

The PUMPING DOWN message indicates that a
compressor in the respective system is presently in the
process of pumping the system down. When pumpdown
is initiated on shutdown, the liquid line solenoid or EEV
will close and a compressor will continue to run. When
the suction pressure decreases to the suction pressure
cutout setpoint or runs for 180 seconds, whichever
comes

rst, the compressor will cycle off.

Fault Safety Status Messages

Safety Status messages appear when safety thresholds
in the unit have been exceeded. Safeties are divided
into two categories – system safeties and unit safeties.
System safeties are faults that cause the individual
system to be shut down. Unit safeties are faults that cause
all running compressors to be shut down. Following are
display messages and explanations.

System Safeties

System safeties are faults that cause individual systems
to be shut down if a safety threshold is exceeded for 3
seconds. They are auto reset faults in that the system
will be allowed to restart automatically after the fault
condition is no longer present. However, if 3 faults on
the same system occur within 90 minutes, that system
will be locked out on the last fault. This condition is then
a manual reset. The system switch (under OPTIONS
key) must be turned off and then back on to clear the
lockout fault. Fault messages will be displayed whenever
a system is locked out.

The Discharge Pressure Cutout is a software cutout in
the microprocessor and is backed-up by a mechanical
high pressure cutout switch located in the refrigerant
circuit. It assures that the system pressure does not
exceed safe working limits. The system will shutdown
when the programmable cutout is exceeded and will be
allowed to restart when the discharge pressure falls 40
PSIG below the cutout.

Discharge transducers must be

installed for this function to operate.

S Y S 1 P U M P I N G D O W N

S Y S 2 P U M P I N G D O W N

S Y S 1 M P / H P C O F A U L T

S Y S 2 M P / H P C O F A U L T

S Y S 1 M P / H P C O I N H I B

S Y S 2 M P / H P C O I N H I B