Thermo King CRR-40 119, Manual

Page: 57 / 170

MP-3000a Controller
57
Initial Unit Start-up and Normal Operation
(Standard)
Power Limit is active during the compressor
start-up in both the Chill and Frozen modes.
During start-up, the controller partially closes the
KVQ valve to reduce the cooling capacity load on
the compressor. The actual KVQ Setting depends
on the condenser temperature, but ranges between
10 C and 30 C (5.6 and 16.8 F) below the return
air temperature. The KVQ valve then gradually
opens to increase cooling capacity during initial
pull-down as required.
When the total current or the condenser
temperature exceeds a predetermined threshold,
the controller limits unit power consumption by
sending a voltage pulse to the KVQ valve. The
KVQ valve closes to restrict the flow of
refrigerant to the compressor to limit the
compressor motor current draw and the condenser
temperature to the predetermined threshold.
Power Limit Management
Additional power limit management flexibility is
available. A maximum total current draw (17, 15
or 13 amps) and power management time interval
can be selected from the Power Management
feature of the Commands menu. When the power
management time interval expires, the unit returns
to the standard power limit control algorithm.
NOTE: Setting power management current at 13
amps can be used to provide slow pull-down of
loads.
Evaporator Fan Control
The controller determines evaporator fan motor
speed based on the setpoint temperature and the
Economy mode setting.
• Evaporator fans operate on HIGH speed at
setpoints of -9.9 C (14.1 F) and above. If
the Economy mode is ON and temperature
is In-range, the controller shifts the
evaporator fans to LOW speed.
• Evaporator fans operate on LOW speed at
setpoints of -10 C (14 F) and below. If the
Economy mode is ON and the unit is in
the Null mode, the controller STOPS the
evaporator fans. The controller then
operates the evaporator fans on LOW
speed for 5 minutes every 45 minutes as
long as the unit remains in the Null mode.
Condenser Fan Control
The controller also uses a proportional-integral
derivative algorithm to control the condenser
temperature and ensure a constant liquid pressure
at the expansion valve. In low ambient conditions,
the controller pulses the condenser fan ON and
OFF to maintain a minimum condenser
temperature. The controller maintains a minimum
30 C (86 F) condenser temperature on Chill loads
and a minimum 20 C (68 F) condenser
temperature on Frozen loads.
Economy Mode Operation
The Economy Mode reduces unit power
consumption by reducing evaporator fan
operation on both chill and frozen loads. The use
of the Economy Mode should be established by
the shipper and the type of cargo. The Economy
Mode option is turned on from Setpoint menu of
the controller.
NOTE: Enter Setpoint temperature before
turning ON the Economy mode. The controller
automatically turns the Economy mode OFF
when the setpoint is changed.
Chill Loads (Setpoints of -9.9 C (14.1 F)
and Above)
Evaporator fans operate on low speed whenever
the container temperature is In-range.
NOTE: On Chill loads, container air
temperatures may vary 1 C to 3 C (1.8 F to 5.4 F)
above setpoint in high ambient temperatures.
Frozen Loads (Setpoints of -10 C (14 F)
and Below)
The evaporator fans stop during the Null mode. A
null state timer automatically re-starts the
evaporator fans on low speed for 5 minutes every
45 minutes.