62-113894−15
unless the compressor is restarting following a defrost
cycle. If the compressor discharge temperature (CDT)
becomes greater than 284°F (140°C) or the system re-
turns to Pulldown mode 10 minute will be overridden and
the unloaders will de-energize (load) as required.
4. Fan Motor Delay.
Whenever any fan motor has been energized, there will
be a 3 second delay before either unloader is allowed to
de-energize (load).
5. Four Cylinder Delay.
When the compressor suction pressure (CSP) is great-
er than 22 psig (1.5 bar) AND the compressor is fully un-
loaded (operating on 2 cylinders), AND the conditions
call for UL2 to be de-energized (loaded), there will be a
20 second delay while the CSMV closes down by 20%
from the current setting. After UL2 loads the CSMV will
go back to normal control.
6. Two-Minute Delay.
When an unloader is energized (unloaded) due to a re-
frigeration system pressure override (overrides #6, 7, 8
or 9), the unloader remains energized for a minimum of
2 minutes.
7. Compressor Startup.
UL1 remains energized (unloaded) for a minimum of
10 seconds when the ambient is above 100°F
(37.8°C) or 5 seconds when the ambient is at or below
100°F (37.8°C) after the compressor motor contactor
is energized
UL2 remains energized (unloaded) for a minimum of
60 seconds when the ambient is above 100°F
(37.8°C) or 30 seconds when the ambient is at or be-
low 100°F (37.8°C) after the compressor motor con-
tactor is energized
8. High Evaporator Pressure.
UL2 will always be energized (unloaded) when the
suction pressure is above the value shown Figure 4−6
for 1 minute, according to the current ambient
temperature. For example, at an ambient temperature
of 100°F (37.8 °C), UL2 will be energized when the
suction pressure rises to approximately 75 psig (5 bar).
UL2 can load as soon as the pressure is 5 psig (0.3 bar)
less than the value in the chart.
9. High Discharge Pressure.
If the compressor discharge pressure reaches 435
psig (29.6 bar) at some point soon after engine start
up for more than 1 minute, UL2 will energize (unload)
and remain energized until the compressor discharge
pressure drops below 415 psig (29.6 bar).
If both unloaders are energized (unloaded), and the
discharge pressure drops below 430 psig (29.3 bar),
UL1 will be de-energized (loaded)
10.Low Suction Pressure.
If suction pressure falls below -2 psig or 4 inHg (0.14
bar) for more than 20 seconds, UL2 will be energized
(unloaded)
After 20 seconds: if suction pressure is still less than
-2 psig or 4 inHg (0.14 bar), UL1 will be energized (un-
loaded), OR
Once the suction pressure rises above 5 psig (0.3
bar), UL2 will be de-energized (loaded) (after the
2-Minute Delay mentioned above)
If both unloaders are energized (unloaded), AND 20
seconds has elapsed since energizing (unloading)
UL1 AND the suction pressure rises above 5 psig (0.3
bar), UL1 will be de-energized (loaded)
11.High CDT.
If the compressor is operating with both unloaders
energized (unloaded), and the CDT rises to 284°F
(140°C), UL1 will be de-energized (loaded), and will
remain de-energized (loaded) until the CDT drops
below 266°F (130°C) for at least 2 minutes.
12.Cargo Protect Mode.
Refer to Section 4.8.1
13.Start-Stop Operation.
If the Off Cycle conditions have been met in Start-Stop
Mode (Refer to Section 4.4) and the minimum run time
has expired, BUT compartment temperature is not at
set point, both unloaders will be de-energized (loaded)
and the compressor will operate on 6-cylinders until the
unit cycles off.
0
20
40
60
80
100
90 100 110 120 130 140
PSIG
Ambient Temperature (5F)
Figure 4−6 Evaporator Pressure Chart
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