Indoor Expansion Valve
The Indoor Expansion Valve (EVI) is a 12 VDC stepper motor
driven valve, used in heating and cooling mode. In cooling
mode EVI is used to expand the refrigerant entering the Indoor
Coil, operating as an evaporator, in much the same way as a
TXV on a conventional air conditioner. In heating mode the EVI
can operate in two different modes, configurable at the keypad.
When configured for Standard during heating mode the EVI
will modulate to fully open and remain in this position. When
configured for heating mode the EVI will modulate to maintain
the Subcooling Set-Point.
DPS 016–028 unit use only an EVI to control suction super
heat.
Figure 32: Indoor Expansion Valve
Outdoor Expansion Valve (DPS 003–015 only)
The Outdoor Expansion Valve (EVO) is a 12 VDC stepper
motor driven valve, used in heating and cooling mode. Cooling
only units will not have this component, only Heat Pumps.
In heating mode the EVO is used to expand the refrigerant
entering the Outdoor Coil, which is now and evaporator,
in much the same way as a TXV on a conventional air
conditioner. In Cooling Mode the EVO can operate in two
different modes, configurable at the keypad. When configured
for Standard during Cooling Mode the EVO will modulate
to fully open and remain in this position. When configured
for Cooling Mode the EVO will modulate to maintain the
Subcooling Set-Point.
The outdoor expansion valve will regularly require an
automated synchronization to maintain valve and motor
alignment. Whenever the valve is commanded to either 0 or
100% the valves will automatically be over-driven closed or
open by 10% of the maximum steps as defined by the motor,
unless otherwise not recommended by manufacturer, then the
process will only occur on 0% closed calls. In the event of a
power interruption or indications of loss of synchronization,
the MicroTech III controller can force synchronization to
correct operation.
Suction Pressure Transducer
The Suction Pressure Transducer (PTS) is a refrigerant
pressure sensor that screws onto a Schrader fitting on the
suction line of the compressor deck. On single compressor
units (3–6T) this sensor is located on the suction line. On
tandem, two compressor units (7–15T), the PTS is located
upstream of the joint suction.
This sensor is used to ensure that the compressor does not
leave the operating envelope and is used to regulate the super
heat leaving the indoor coil and entering the compressor.
Discharge Pressure Transducer
The Discharge Pressure Transducer (PTD) is a refrigerant
pressure sensor that screws onto a Schrader fitting on
the discharge line of the compressor system. On single
compressor units (3–6T) this sensor is located on the
discharge line. On tandem, two compressor units (7–15T), the
PTD is located down stream of the joint discharge.
This sensor is used to ensure that the compressor does not
leave the operating envelope and is used to regulate the
outdoor fan speed and maintain head pressure.
Discharge Refrigerant Temperature
All Rebel units will have a Discharge Refrigerant Temperature
Sensor (DRT1 / DRT3) on the discharge line of each
compressor. This sensor is attached the piping with a metal
clip and wrapped in insulation. The purpose of this device is to
increase compressor life by preventing it from running outside
of the operating envelope.
Suction Refrigerant Temperature
All Rebel units will have a Suction Refrigerant Temperature
Sensor (SRT). This sensor is located on the suction line. Unlike
DRT1 or 3 there is only one SRT for tandem compressor
units. This sensor is used to determine the suction super heat
entering the compressor and is the control input for the EVI in
cooling mode (EVO in heating mode).
Indoor Refrigerant Temperature (DPS 003–015 only)
Only Rebel Heat Pump units will have an Indoor Refrigerant
Temperature Sensor (IRT). This sensor is used in Heating
Mode when htgEVImethod is set to control subcooling. This
sensor is attached to the refrigerant piping downstream
(Cooling Mode) of the Indoor Expansion Valve (EVI).
Indoor
Indoor
Refrigerant
Refrigerant
Temperature
Temperature
Sensor (IRT)
Sensor (IRT)
Indoor
Indoor
Expansion
Expansion
Valve (EVI)
Valve (EVI)
Refrigeration System
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IM 1125-13 • REBEL ROOFTOPS