Electrical Maintenance
56
High Capacity TherMax
TM
Heating System
The high capacity heating system increases the
capacity of the Heat mode by making more
refrigerant available for use in the Heat mode.
This is accomplished by adding an additional
solenoid (TherMax
TM
solenoid) to the
refrigeration system which opens during the
beginning of the Heat mode to move the liquid
refrigerant from the condenser to the accumulator
where it can be used in the Heat mode. The
sequence of operation for the improved heating
system is from the Cool mode to the Heat mode
with Refrigerant Transfer mode to the Heat mode.
The Heat mode to Cool mode operation is the
same as in the past. The bypass check valve, and
the condenser check valve have been eliminated
from the TherMax
TM
heating system.
The components that have been added to the
system are:
• the TherMax
TM
solenoid
• the TherMax
TM
solenoid line
• the receiver outlet check valve
The TherMax
TM
solenoid controls the flow of
refrigerant through the TherMax
TM
solenoid line.
The TherMax
TM
solenoid line goes from the liquid
line just past the receiver outlet check valve to the
accumulator inlet. The receiver outlet check valve
is located in the liquid line near the drier/receiver
outlet. This check valve prevents refrigerant from
migrating back into the receiver tank and
condenser during the Heat mode.
Cool Mode
The Cool mode has not been changed in the
TherMax
TM
heating system. The TherMax
TM
solenoid, which is normally closed, is
de-energized during the Cool mode. The
TherMax
TM
solenoid separates the high side from
the low side. When the TherMax
TM
solenoid is
closed, it does not allow liquid refrigerant to flow
from the liquid line, through the TherMax
TM
solenoid line, to the accumulator.
Heat/Condenser Evacuation Mode
The unit will run in the Condenser Evacuation
mode for two minutes before entering the Heat
mode. This is accomplished by opening
(energizing) the TherMax
TM
solenoid while the
unit is running in cool. The pressure difference
between the high pressure in the condenser and
the low pressure in the accumulator drives much
of the refrigerant out of the condenser and
receiver into the accumulator. The refrigerant is
then available for improved heating capacity. The
unit is placed in the Heat mode by opening
(energizing) the hot gas solenoid and closing
(energizing) the condenser inlet solenoid. The
TherMax
TM
solenoid remains open while the unit
is in the Heat mode. The receiver outlet check
valve prevents the migration of refrigerant back
into the receiver tank and condenser.
Defrost Mode
The Condenser Evacuation mode is not used
before the Defrost mode. The TherMax
TM
solenoid, the hot gas solenoid, and the condenser
inlet solenoid are all energized at the same time.
The TherMax
TM
solenoid remains open while the
unit is in the Defrost mode.
Start Up Mode
For the first 20 seconds when the unit is started it
runs in the Cool mode with the TherMax
TM
solenoid open and the alternator excitation circuit
(7K) de-energized. This reduces the load. The
Start Up mode is used for both diesel and electric
operation.
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