JOHNSON CONTROLS
207
SECTION 7 - OPERATION
FORM 201.23-NM2
ISSUE DATE: 09/25/2020
7
TABLE 9 - DISCHARGE PRESSURE LOAD
LIMITING/UNLOADING
DISCHARGE PRESSURE UN-LOADING
Discharge Pressure Cutout- 20 psig
&
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 Cutout plus 2 psig. Between Cutout
plus 2 psig and the Cutout, loading is inhibited, even
though increased loading is required. Between the
Suction pressure Cutout and Suction Pressure Cutout
minus 10 psig, forced unloading is performed every
2 seconds according to Table 10 on page 207. This
situation would occur if the suction pressure cutout
transient override control is in effect (See “Low Suc-
tion Pressure Cutout”, Page 247). The suction pressure
cutout is programmed under the PROGRAM key. The
default Suction Pressure Cutout is set at 24.0 psig.
TABLE 10 - SUCTION PRESSURE LOAD LIMITING/
UNLOADING
SUCTION PRESSURE UN-LOADING
Suction Pressure is between
Cutout +2 psig &
Suction Pressure Cutout
0 Hz
Suction Pressure Cutout- 1 psig 1 Hz
Suction Pressure Cutout- 2 psig 2 Hz
Suction Pressure Cutout- 3 psig 3 Hz
Suction Pressure Cutout- 4 psig 4 Hz
Suction Pressure Cutout- 5 psig 5 Hz
Suction Pressure Cutout- 6 psig 6 Hz
Suction Pressure Cutout- 7 psig 7 Hz
Suction Pressure Cutout- 8 psig 8 Hz
Suction Pressure Cutout- 9 psig 9 Hz
Suction Pressure Cutout- 10 psig 10 Hz
Suction pressure load limiting is active at start-up, 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.
VSD Internal Ambient Temperature Load
Limiting
VSD Internal Ambient temperature limiting helps pre-
vent the unit from tripping on the high internal cabinet
temperature safety. A system is permitted to load nor-
mally as long as the VSD Internal Ambient is below
the VSD Internal Ambient Cutout minus 3°F. Between
VSD Internal Ambient Cutout minus 3°F and the VSD
Internal Ambient Cutout minus 2°F, loading is inhibit-
ed, even though increased loading is required. Between
the VSD Internal Ambient Cutout minus 2°F and the
VSD Internal Ambient Cutout, forced unloading is per-
formed every 2 seconds according to Table 11 on page
207 below. The VSD Internal Ambient Safety Cutout
is 158°F.
TABLE 11 - VSD INTERNAL AMBIENT LOAD
LIMITING/UNLOADING
VSD INTERNAL
AMBIENT TEMPERATURE
UN-LOADING
Internal Ambient Temp. is between
Cutout- 3ºF & Internal Ambient Cutout- 2ºF
0 Hz
Internal Ambient Cutout- 1.8ºF 1 Hz
Internal Ambient Cutout- 1.6ºF 2 Hz
Internal Ambient Cutout- 1.4ºF 3 Hz
Internal Ambient Cutout- 1.2ºF 4 Hz
Internal Ambient Cutout- 0ºF 5 Hz
Internal Ambient Cutout- 0.8ºF 6 Hz
Internal Ambient Cutout- 0.6ºF 7 Hz
Internal Ambient Cutout- 0.4ºF 8 Hz
Internal Ambient Cutout- 0.2ºF 9 Hz
Internal Ambient Cutout 10 Hz
VSD Baseplate Temperature Load Limiting
VSD Baseplate load limiting helps protect the unit
from tripping on the high VSD Baseplate Temp Safety.
A system is permitted to load normally as long as the
VSD Baseplate temperature is below the VSD Base-
plate Temperature Cutout minus 8°F. Between the VSD
Baseplate Temperature Cutout minus 8°F and the VSD
Baseplate Temperature Cutout minus 4°F, loading is
inhibited, even though increased loading is required.
Between the VSD Baseplate Temperature Cutout mi-
nus 4°F and the cutout, forced unloading is performed
every 2 seconds according to Table 12 on page 208.
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