MP-3000 Controller
61
Frozen Loads: (Setpoint at -10 C
[14 F] and Below)
The unit operates on Full Cool and Null to
provide accurate control of frozen cargo. The
controller uses the return air sensor temperature
and setpoint temperature to regulate unit
operation.
If the return air sensor becomes disconnected or
fails, the controller uses the supply air sensors
plus an offset for temperature control.
Modulation Display in Data Menu
The percent displayed in the Data menu indicates
the modulation capacity that is currently provided.
For example, when controller display shows 70%,
this means the stepper motor valve has closed to
reduce system cooling capacity from 100% to
70% (a 30% reduction).
Power Limit Mode
The controller uses the total unit current and the
condenser temperature to provide power limit
control in both the Chill and Frozen modes. When
the unit is on water-cooled operation, power limit
control is based on the total unit current draw
only.
Initial Unit Start-up and Normal Operation
(Standard)
Power Limit is active whenever the compressor is
on in both the Chill and Frozen modes. When the
total current draw or the condenser temperature
exceeds a predetermined threshold, the controller
limits unit power consumption by sending a
voltage pulse to the stepper motor valve. The
stepper motor valve then closes to restrict the flow
of refrigerant to the compressor. This reduces the
cooling capacity load on the compressor, thereby
limiting the compressor motor current draw and
the condenser temperature to a 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.
Compressor Liquid Injection
During compressor operation, a liquid injection
system injects refrigerant into the center scroll of
the compressor to protect against excessively high
operating temperatures. When liquid injection is
active, the controller energizes the liquid injection
valve continuously. The controller activates liquid
injection when the:
• Chill or Power Limit Mode: When the
modulation capacity is 91% or less (in the
Data menu display), the controller energizes
liquid injection valve continuously.
• Compressor discharge temperature exceeds
128 to 138 C (262 to 280 F). Liquid injection
stops when the compressor discharge
temperature decreases 6 C (10.7 F).
High Temperature Protection
If the discharge gas temperature rises above 148 C
(298 F), the unit stops immediately. The controller
turns on the Alarm LED and records Alarm 56
(Compressor Temperature Too High). The
controller will restart the unit when the sensor
temperature is below 90 C (194 F).
Warm Gas Bypass
During Chill Mode operation, a warm gas bypass
system diverts refrigerant from the high side to
the suction line as the supply air temperature
decreases toward setpoint. This reduces unit
cooling capacity and increases refrigerant flow
through the compressor. The controller energizes
(opens) the warm gas bypass valve when the
modulation capacity is approximately 50% or
less. Modulation capacity can be viewed in the
Data menu display of the controller.
To Next Page
Loading...
Need help?
General
