SECTION 7 - OPERATION
JOHNSON CONTROLS
129
Form 201.28-NM1.1
Issue date: 08/06/2021
7
The discharge pressure unload point is fixed at 255
psig.
Table 18 -
Discharge pressure load limiting/unloading
Discharge pressure
Unloading
Discharge Pressure Cut-
out- 20 psig and Discharge
Pressure Cutout- 15 psig
0 Hz
Discharge Pressure Cutout- 13.5 psig
1 Hz
Discharge Pressure Cutout- 12 psig
2 Hz
Discharge Pressure Cutout- 10.5 psig
3 Hz
Discharge Pressure Cutout- 9 psig
4 Hz
Discharge Pressure Cutout- 7.5 psig
5 Hz
Discharge Pressure Cutout- 6 psig
6 Hz
Discharge Pressure Cutout- 4.5 psig
7 Hz
Discharge Pressure Cutout- 3 psig
8 Hz
Discharge Pressure Cutout- 1.5 psig
9 Hz
Discharge Pressure Cutout- 0 psig
10 Hz
Suction pressure load limiting/unloading
Suction pressure load limiting helps to protect the
evaporator from freezing. A system is permitted to
load normally as long as the Suction Pressure is above
the "Suction Pressure 2.6 psig". Between
"Suction Pressure 2.6 psig" and the "Suction
Pressure 1.7 psig", loading is inhibited, even
though increased loading is required.
Between the "Suction Pressure 1.7 psig" and
"Suction Pressure Cutout", forced unloading is per-
formed every 2 seconds according to
. This situation would occur if the suction pres-
sure cutout transient override control is in effect (See
Low Suction Pressure Cutout (Software) Fault on Page
). The suction pressure cutout is programmed un-
der the PROGRAM key. The default Suction Pressure
Cutout is set at 26.1 psig.
Suction pressure load limiting is active at startup, to
only prevent loading of the compressors. Suction pres-
sure limit unloading will not occur until the system run
time reaches 5 minutes of operation to allow the sys-
tem to stabilize.
Table 19 -
Suction pressure load limiting/unloading
R-134A
Suction pressure
Unloading
Suction Pressure is between
"2.60 psig" and
"1.70 psig"
0 Hz
Suction Pressure 1.53 psig
1 Hz
Suction Pressure 1.36 psig
2 Hz
Suction Pressure 1.19 psig
3 Hz
Suction Pressure 1.02 psig
4 Hz
Suction Pressure 0.85 psig
5 Hz
Suction Pressure 0.68 psig
6 Hz
Suction Pressure 0.51 psig
7 Hz
Suction Pressure 0.34 psig
8 Hz
Suction Pressure 0.17 psig
9 Hz
Suction Pressure Cutout
10 Hz
R-513A
Suction pressure
Unloading
Suction Pressure is between
"2.70 psig" and
"1.80 psig"
0 Hz
Suction Pressure 1.62 psig
1 Hz
Suction Pressure 1.44 psig
2 Hz
Suction Pressure 1.26 psig
3 Hz
Suction Pressure 1.08 psig
4 Hz
Suction Pressure 0.90 psig
5 Hz
Suction Pressure 0.72 psig
6 Hz
Suction Pressure 0.54 psig
7 Hz
Suction Pressure 0.36 psig
8 Hz
Suction Pressure 0.18 psig
9 Hz
Suction Pressure Cutout
10 Hz
Sensor failure cutout fault
The Sensor Failure Cutout prevents the system from
running when a critical sensor (transducer, level sen-
sor, or motor winding temp sensor) is not function-
ing properly and reading out of range. This safety is
checked at startup and will prevent the system from
running if one of the sensors has failed.
The sensor failure safety will also fault and shutdown
a system while in operation, if a safety threshold is ex-
ceeded or a sensor reads out of range (high or low).
Following is the Status display fault message.
SYS X YYYYYYYY SENSOR FAILURE:
ZZZZZZZZZZZZ