Thermo King 098916, Maintenance Manual

Page: 107 / 196

Operating Theory
106
controller energizes the vapor injection valve
continuously. The controller activates vapor
injection when the:
• Chill or Power Limit Mode: When the cool
capacity is 100 percent (in the Data menu
display), the controller energizes the vapor
injection valve continuously.
• Compressor discharge temperature exceeds
138 C (280 F). Vapor 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 Code
56 (Compressor Temperature Too High). The
controller will restart the unit when the sensor
temperature is below 90 C (194 F).
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.
Evaporator Fan Control
The controller determines evaporator fan motor
speed based on the setpoint temperature and the
Economy mode setting.
Chill Loads (Setpoints of -9.9 C [14.1 F] and
Above)
When the Economy mode is set to Off, the
evaporator fans operate continuously on high
speed.
Frozen Loads (Setpoint at -10.0 C [14.0 F] or
Below)
When the Economy mode is set to Off, the
evaporator fans operate on low speed. Low speed
RPM is one-half the high speed RPM.
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): When the temperature is
In-range, the controller shifts the evaporator
fans to low speed.
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): When the unit is in the Null mode,
the controller stops the evaporator fans. A null
state timer automatically re-starts the
evaporator fans on low speed for 5 minutes
every 45 minutes.
The Economy mode also modifies the temperature
control algorithm on frozen loads to extend the
Null mode. The unit continues on Cool operation
until return air temperature reaches ECMIN
temperature. Default ECMIN setting is 2.0 C
(3.6 F) below setpoint. ECMIN temperature is
adjustable from 0 to 5 C (0 to 8.9 F) below
setpoint through the Configuration menu of the
controller.
The unit remains in Null until the return air
temperature increases to ECMAX temperature at
the expiration of a 45 minute Null state time
sequence. Default ECMAX setting is 0.2 C (0.4 F)
above setpoint. ECMAX setting is adjustable
from 0 to 5 C (0 to 8.9 F) above setpoint through
the Configuration menu of the controller.
NOTE: On Frozen loads, supply and return air
temperatures may vary considerably during
Economy mode operation due to long periods of
no air circulation.