York MILLENNIUM YCAS Installation Operation & Maintenance page 113

pressor will shut down if the discharge temperature ex-
ceeds 127°C (260ºF).
High Oil Differential Pressure Cutout:
S Y S # H I G H
S Y S # H I G H
The High Oil Pressure Differential Safety protects the
compressors against loss of proper lubrication due to oil
return line blockage. The "differential oil pressure" for
this safety is computed by measuring discharge (oil sepa-
rator) pressure and subtracting oil pressure returning to
the compressor (Discharge - Oil = Oil PSID). Under
typical operation, the oil pressure differential display will
read less than 1.7 bar (25 PSID). If oil pressure at the
compressor drops due to filter blockage, the differential
pressure on the display will increase and when the maxi-
mum limit is reached the compressor will be shut down.
This safety is activated after 3 minutes of operation. Oil
pressure must be less than 4.4 bar (65 PSID) for R22
models as long as the compressor continues to run.
Low Oil Differential Pressure Cutout:
S Y S # L O W
S Y S # L O W
The Low Oil Pressure Differential Safety assures the
compressor receives proper lubrication by monitoring
the differential between oil pressure returning to the
compressor and suction pressure. Lack of a differential
indicates that the compressor is not pumping and no oil
is being pumped through the compressor to lubricate
the bearings and rotors.
This type of oil failure will not be picked up by the High
Oil Differential Safety since no flow will cause the dif-
ferential through the oil piping to drop to zero.
Example:
For ambients above 10°C (50ºF), the Low Oil Differen-
tial Safety is activated after 1 minute of compressor
operation when the oil pressure differential must be
greater than 0.7 bar (10 PSID). After 2 minutes it must
be greater than 1.4 bar (20 PSID); after 3 minutes, 2
BAR (30 PSID); after 4 minutes, 2.7 bar (40 PSID);
and from 5 minutes of operation and onwards, oil pres-
sure must remain higher than 3.4 bar (50 PSID) or the
system will be shut down. For lower ambients, the lin-
ear ramp times are as follows:
YORK INTERNATIONAL
O I L D I F F
O I L D I F F
O I L D I F F
O I L D I F F
AMBIENT TEMP
>10ºC (50ºF)
>7ºC (45ºF)
>4ºC (40ºF)
>2ºC (35ºF)
>-1ºC (30ºF)
<= -1ºC (30ºF)
High Oil Temperature Cutout:
S Y S # H I G H
S Y S # H I G H
This safety assures oil temperature does not exceed a
safe operating temperature which affects compressor
lubrication. Typical oil temperature during normal op-
eration will be approximately 54 - 66°C (130 - 150ºF).
The High Oil Temperature Safety is activated after 2
minutes of compressor operation, after which if oil tem-
perature is above 107°C (225ºF) for more than 3 sec-
onds, the compressor will shut down.
Low Suction Pressure Cutout:
S Y S # L O W
S Y S # L O W
The Low Suction Pressure Cutout aids in protecting
the evaporator from damage due to ice build up caused
by operation at low refrigerant charge or restricted re-
frigerant flow. A number of transient timer features pre-
vent nuisance trips during start-up, compressor loading,
etc. The Low Suction Pressure Safety is programmable
(see Section 8.2 / Page 130, Low Suction Pressure
Cutout for more details).
The suction pressure cut-out is ignored for the first 45
seconds of operation. During the next 180 seconds of
running , suction pressure may be lower than the cut-
out, but must be greater than:
Programmed Cutout * (run Time - 25)
SP Cutout =
This cutout value increases with time until after 225
seconds it equals the programmed cutout value. If suc-
tion pressure falls below the calculated cutout value
before 225 seconds of run time, the system will be shut
down.
FORM 201.18-NM2
RAMP TIME
5 Minutes
6 Minutes
7 Minutes
8 Minutes
9 Minutes
10 Minutes
O I L T E M P
O I L T E M P
S U C T P R E S S
S U C T P R E S S
25
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