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As the system operates in the Heat Mode with SV2
closed, discharge pressure tends to decrease. As the
system operates in the Heat Mode with SV2 open dis-
charge pressure tends to increase. Control of the valve
is dependent on discharge pressure and ambient tem-
perature. The valve is opened (on a discharge pres-
sure fall) at 200 PSIG (13.6 bar), the valve is closed
(on a discharge pressure rise) at 300 PSIG (20.4 bar).
When the ambient temperature is below 50°F (10°C)
SV2 will be opened when discharge pressure
decreases to the opening pressure and remain open
until discharge pressure rises to the close pressure.
When the ambient temperature is above 50°F (10°C)
SV2 will be pulsed, open for one second and then
closed for 10 seconds. During the 10 second closed
period the system pressures will be allowed to balance
out due to the additional refrigerant in the hot gas
cycle. The pulse will continue, one second open and
ten seconds closed, until discharge pressure increases
to the close pressure.
4.4.4
UltraFresh Temperature Control
UltraFresh 3 is an advanced method of temperature
control for both Perishable and Frozen ranges. It pro-
duces a reduced capacity state by throttling the CSMV
and pulsing the refrigerant control solenoid valves.
UltraFresh uses both the supply and return air sensors
to control compartment temperature.
The sensor selected in the TEMP CONTROL Func-
tional Parameter is the probe that will be used to deter-
mine when the temperature is at setpoint.
Reduced capacity is produced between heating and
cooling by a set of modes known as Cool Pulsed Mode,
Heat Pulsed Mode and Null Pulsed Mode. These
modes are not constant operating modes, they operate
for a few seconds at a time. During null, the heat and
cool valves are opened simultaneously to reduce either
the heating or cooling capacity. In these modes (Refer
to the following charts), the unit will pulse between cool
and null, or heat and Null in 10 second increments. The
capacity is varied by adjusting the pulse rate.
a. Cool Pulsed Mode
Note: For CSMV/EVXV control, see following step d.
b. Null Pulsed Mode
Note: For CSMV/EVXV control, see following step d.
c. Heat Pulsed Mode
Note: For CSMV/EVXV control, see following step d.
UltraFresh will modify the length of each mode in 10
second cycles. That is, if the unit is in Cool Pulse
Mode, the unit may run in cool for up to nine seconds,
then null for one second, if the Control Temperature is
away from setpoint. As the Control Temperature
comes closer to setpoint, the length of cool pulse time
will decrease, and the amount of null time will increase.
However, the combination of the two will always equal
10 seconds. The same is true for the Heat Pulse Mode.
d. UltraFresh 3 CSMV/EVXV control
The CSMV will automatically go to 30% when Ultra
Fresh 3 is entered. The CSMV will usually control
between 30% and 4% depending on the controlling
probe temperature and suction pressure. However, it
can go above 30% for short periods of time. For exam-
ple, high ambients and low setpoints may cause the
CSMV to open higher than 30%. The EVXV will be
modulated to control superheat when in cooling and
100% open in heating.
4.4.5
UltraFreeze Temperature Control
For frozen setpoints, a modified temperature control
will be used to keep the unit from over cooling and driv-
ing the box temperature far below setpoint. UltraFreeze
operates similar to UltraFresh and acts to control the
compartment temperature from exceeding 3° F (1.6° C)
below setpoint When UltraFreeze is active it is normal
to hear the refrigerant solenoid valves energize and de-
energize every few seconds. UltraFreeze is always
active in Continuous Operation, should the unit be
required to continue to run after the box temperature is
satisfied in Start-Stop Operation - due to either low bat-
tery condition or low engine coolant temperature - the
UltraFreeze logic will control to the 3° F (1.6° C) below
setpoint offset until all conditions for an off cycle are
met and the unit cycles off.
4.4.6
Defrost
for a description of defrost.
4.4.7
Overrides
With the complex control interactions in use with the
APX control system there are many user selected and
preprogrammed software overrides and Configuration
settings which may change the operation of the unit.
Refer to
for complete
descriptions of these features.
SV1
SV2
SV4
Engine
Speed
Open
Open
Closed
Low
Clutch
Output
UL1 & UL2
CSMV/
EVXV
Engage
Unload
See Note
SV1
SV2
SV4
Engine
Speed
Open
Open
Open
Low
Clutch
Output
UL1 & UL2
CSMV/
EVXV
Engage
Unload
See Note
SV1
SV2
SV4
Engine
Speed
Closed
Closed
Open
Low
Clutch
Output
UL1 & UL2
CSMV/
EVXV
Engage
Unload
See Note
Содержание Transicold X4 7300
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