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Unit Controls
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.
S Y S
1
H I G H
S Y S
2
H I G H
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 cir-
cuit. It assures that the system pressure does not ex-
ceed safe working limits. The system will shutdown when
the programmable cutout is exceeded and will be al-
lowed to restart when the discharge pressure falls below
the cutout. Discharge transducers must be installed for
this function to operate.
S Y S
1
L O W
S Y S
2
L O W
The Suction Pressure Cutout is a software cutout that
protects the unit from an evaporator freeze-up should
the system attempt to run with a low refrigerant charge
or a restriction in the refrigerant circuit.
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
100
D S C H
P R E S
D S C H
P R E S
S U C T
P R E S S
S U C T
P R E S S
time during this 3 minutes the suction pressure falls below
the ramped cutout point, the system will stop. This cut-
out is ignored for the first 90 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 first 3 minutes, if the suction pressure falls
below the programmed cutout setting, a "transient pro-
tection 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 sec-
onds the suction pressure falls below the ramped cut-
out, the system will stop. This transient protection
scheme only works if the suction pressure transducer is
installed. When using the mechanical LP switch, the
operating points of the LP switch are: opens at 23 PSIG
+/- 5 PSIG (1.59 barg +/- .34 barg), and closes at 35
PSIG +/- 5 psig (2.62 barg +/- .34 barg).
S Y S
1
M P / H P C O
S Y S
2
M P / H P C O
The Motor Protector/Mechanical High Pressure Cutout
protects 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 the motor protector opening. This causes the respec-
tive CR contacts to open causing 0VDC to be read on
the inputs to the microboard. The fault condition is cleared
when a 30 VDC signal is restored to the input.
The internal motor protector opens at 185°F (85°C) to
248°F (120°C) and auto resets. The mechanical HP
switch opens at 405 PSIG +/- 10 psig (27.92 barg +/-
.69 barg) and closes at 330 PSIG +/- 25 PSIG (22.75
barg +/- 1.72 barg).
F A U L T
F A U L T
YORK INTERNATIONAL
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