4–7
T-372
4.3.11
Perishable Mode Cooling - Sequence of Operation
NOTE
In Standard Perishable Mode, the evaporator motors run in high speed. In Economy Fan Mode, the
fan speed is varied.
a. When supply air temperature is above setpoint and decreasing, the unit will cool with the condenser fan
motor (CF), compressor motor (CH), and evaporator fan motors (EF) energized, and the white COOL light
illuminated. (See
). Also, if current or pressure limiting is not active, the controller will close con
-
tacts TS to open the economizer solenoid valve (ESV) and place the unit in economized operation.
Figure 4.5 Perishable Mode Cooling
b. When supply air temperature decreases to a predetermined tolerance above setpoint (Cd30), the green IN
RANGE light is illuminated.
c. As air temperature continues to fall, unloaded cooling starts (DUV pulses opens) as the supply air tempera
-
ture approaches setpoint. (See
).
d. When unloaded cooling starts, EEV control will transition from a full cool superheat setpoint to a lower mod
-
ulated cool superheat setpoint. Once unloading starts, the EEV controls evaporator superheat based on the
system duty cycle where instantaneous superheat will vary.
e. When the supply air temperature has fallen to within 1.9°C (3.4°F) of setpoint temperature and the average
capacity of the system has fallen below 70%, the unit will open contacts TS to close the ESV and take the
unit out of economized operation.
f. The controller continuously monitors supply air temperature. Once the supply air temperature falls below
setpoint, the controller periodically records supply air temperature, setpoint and time. A calculation is then
performed to determine temperature drift from setpoint over time. If the calculation determines that cooling
is no longer required, contacts TC and TN are opened to de-energize the compressor motor and the con
-
denser fan motor. In addition the controller will close the EEV.
g. The evaporator fan motors continue to run to circulate air throughout the container. The green IN RANGE
light remains illuminated as long as the supply air temperature is within tolerance of the setpoint.
h. If the supply air temperature increases to 1.0°C (1.8°F) above setpoint and three minutes have elapsed,
contacts TC and TN close to restart the compressor and condenser fan motors in standard mode (non-
economized) operation. The white COOL light is also illuminated.
i. If the average system capacity has risen to 100% during unloaded cooling and three minutes off time has
elapsed, relay TS will energize to open the ESV, placing the unit in economized mode.
j. If the supply air increases more than 2.5°C (4.5°F) above setpoint temperature, the microprocessor will transi
-
tion the evaporator superheat control from modulation back to full cool control.
24 VOLT POWER
ENERGIZED
DE-ENERGIZED
TN
ST
F
HPS
CH
IP-CM
TC
CF
TE
IP-EM1
EF
IP-EM2
HTT
TH
HR
ESV
TS
TV
EF
ES
