Figure 4−6 Evaporator Pressure Chart - Carrier VECTOR 6500 Operation & Service Manual

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.
S 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
S 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.
100
80
60
40
20
0
90 100 110
Ambient Temperature (5F)
Figure 4−6 Evaporator Pressure Chart
4−15
9. High Discharge Pressure.
S 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).
S 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.
S If suction pressure falls below -2 psig or 4 inHg (0.14
bar) for more than 20 seconds, UL2 will be energized
(unloaded)
S 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
S Once the suction pressure rises above 5 psig (0.3
bar), UL2 will be de-energized (loaded) (after the
2-Minute Delay mentioned above)
S 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.
120 130 140
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