Carrier TRANSICOLD VECTOR 8100 Operation & Service Manual Download

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The refrigerant pressure drop caused by the expansion valve is accompanied by a drop in temperature so the low
pressure, low temperature liquid that flows into the evaporator tubes is colder than the air that is circulated over the
evaporator tubes by the evaporator fan. The evaporator tubes have aluminum fins to increase heat transfer;
therefore heat is removed from the air circulated over the evaporator. This cold air is circulated throughout the
refrigerated compartment to maintain the cargo at the desired temperature.

The transfer of heat from the air to the low temperature liquid refrigerant causes the liquid to vaporize.

This low temperature, low pressure vapor passes the evaporator outlet temperature and pressure sensors (EVOT
and EVOP) which aid in calculation of superheat.

The vapor then returns to the compressor through the compressor suction modulation valve (CSMV). The CSMV
controls the flow of refrigerant entering the suction line, thereby matching the load to the compressor capacity.

2.12.2

Economized Mode

In the economized mode the “main” refrigeration system operates the same as in the Standard Mode except the
control system operates (opens) the economizer expansion valve (ECXV). With the economizer expansion valve
operating (see

Figure 2.9

), the capacity of the unit is increased by subcooling the liquid refrigerant entering the

evaporator expansion valve.

Liquid refrigerant for use in the economizer circuit is taken from the main liquid line as it leaves the filter drier. This
liquid refrigerant flows through the economizer expansion valve (ECXV) and the economizer heat exchanger
internal passages absorbing heat from the liquid refrigerant flowing to the evaporator expansion valve. Overall
efficiency is increased because the gas leaving the economizer enters the compressor at a higher pressure,
therefore requiring less energy to compress it to the required condensing conditions.

There are two levels of economized mode, full economized mode and limited economized mode. Limited
economized mode is entered when the control system requests higher capacity than standard mode but system
current limit will not allow full economizer superheat control.

2.12.3

Null Mode

The system will enter null mode during periods where no cooling or heating is required and system is in continuous
run. In null mode the compressor and heaters are shut down while evaporator fans continue to operate.

The system may also enter the null mode while in start stop if required time or battery condition parameters have
not been met.

2.12.4

Liquid Injection Mode

The control system monitors the signal provided by the compressor discharge temperature sensor. If compressor
temperature rises to the limit (refer to

Section 2.8

), the system will enter Liquid Injection Mode. In this mode the

normally closed liquid injection valve (LIV) will be pulsed or opened as required to allow flow of refrigerant into the
economizer line, to cool the compressor.

2.13 HEAT AND DEFROST

In Heat and Defrost Modes, the compressor is de-energized. In Heat Mode, the coil mounted heaters and
evaporator fans are energized. Air flowing over the warm coil is circulated throughout the refrigerated compartment
to maintain cargo at desired temperature.

If the control system is Configured to allow Natural Defrost, and the compartment temperature is above freezing
defrost may be accomplished using a combination of coil heaters and return air. If compartment temperature is
below freezing or not sufficiently warm enough to defrost the coil, the evaporator fans are de-energized and the coil
mounted heaters energized.