Section 2 – SR-2 Hardware Description
REFRIGERATION CONTROL
COMPONENTS
These components are used by the microprocessor
to sense conditions or control operation of the
refrigeration system. The microprocessor
determines the necessary requirements by
considering the setpoint, the software, the
programmable feature and OptiSet
®
settings, and
the information supplied by the sensors.
Discharge Pressure Transducer (DPT)
This transducer supplies the compressor discharge
pressure to the microprocessor. The sense wire is
connected to the microprocessor at J3 via the DPI
wire. The DPP and DPN wires supply power to the
sensor. This sensor is installed on ETV-equipped
units only.
Suction Pressure Transducer (SPT)
This transducer supplies the compressor suction
pressure to the microprocessor. The sense wire is
connected to the microprocessor at J3 via the SPI
wire. The SPP and SPN wires supply power to the
sensor. This sensor is installed on ETV equipped
units only.
High Pressure Cutout Switch (HPCO)
The high pressure cutout switch is located on the
discharge manifold of four cylinder compressors.
The switch is closed with normal pressures and
opens with excessive pressures to shut the unit
down and prevent damage.
Pilot Solenoid (PS)
The microprocessor energizes (opens) the Pilot
Solenoid to shift the 3 way valve to the heat position
during heat or defrost mode operation. The normally
closed Pilot Solenoid is located near the 3 way
valve. The pilot solenoid is energized and LED 8 is
lit when the microprocessor energizes the Pilot
Solenoid Smart FET. This supplies power via the 26
wire to the pilot solenoid. The circuit is protected by
the Smart FET.
Electronic Throttling Valve (ETV)
The Electronic Throttling Valve is capable of opening
and closing incrementally and is installed between
the evaporator and the compressor.
The ETV is controlled directly by the microprocessor
Smart FET outputs. As the temperature approaches
setpoint, the ETV begins to close, throttling the
suction gas returning to the compressor and thus
reducing cooling capacity. As the box temperature
approaches setpoint, the ETV becomes more nearly
closed. This feature provides very smooth and
steady temperature control. Modulation is only
operational in Continuous mode. The circuit is
protected by the ETV Smart FETs.
2-24
31 January 2005
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