JOHNSON CONTROLS
219
SECTION 7 - OPERATION
FORM 201.23-NM2
ISSUE DATE: 3/9/2015
7
TABLE 7 - 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 Cut-
out 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 8 on page 219. 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 8 - 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 9 on page
219 below. The VSD Internal Ambient Safety Cutout
is 158°F.
TABLE 9 - 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 10 on page 220.
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