Volta Air Technology Owner’s Manual
Van Refrigeration & Freezer Unit
18
CONFIDENTIAL
Refrigeration cycles
Cooling Cycle
In cooling mode system works as a vapor compression refrigeration cycle. Compressor pushes
the high pressure/temperature refrigerant through the condenser coil. Superheated refrigerant
passes some heat to ambient air through the condenser heat exchanger coil and turn to liquid.
Subcooled liquid gets clean and dry in receiver-drier and goes to TXV (thermostatic expansion
valve). The externally equalized TXV drops the refrigerant pressure and meters the flow rate
through the evaporator coil based on the available heat load. Saturated refrigerant turns to vapor
passing through the evaporator coil by absorbing the heat from the air and comes back to
compressor suction inlet. Evaporator fans circulate the cooled air inside the refrigerated box to
cool down the products.
Null mode
Once the box temperature reaches the set point, the system enters the null mode to maintain
the desired temperature. It means the compressor and condenser fan stay off until the box
temperature raises certain amount of degrees higher than the set point temperature and then
system automatically switches to cooling mode.
Defrost / Heating cycle
Defrost is necessary to remove the frost and ice built up on the evaporator coil from the
condensed air moisture during the cooling cycle. Frost formation reduces the evaporator unit
performance significantly by blocking the air circulation passed between the evaporator fins thus
lowering the heat transfer rate. To melt and drain the frosted water, the control system bypasses
the condenser coil and TXV in refrigerant cycle and hot gas sent directly from compressor to
evaporator while evaporator fans are off. This happens by energizing couple of solenoid valves,
HGSV (hot gas solenoid valve) and CPCV (condenser pressure control valve) during defrost cycle.
The main difference between heating and defrost cycle is that the evaporator fan continue
running in heating mode to circulate the warmed air throughout the box. Control system may
switch to null mode during heating if box temperature reaches the set point.
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