Refrigeration Maintenance
133
Electronic Throttling Valve
(ETV)
The Electronic Throttling Valve (ETV) is standard
on the these units. The Electronic Throttling Valve
(ETV) is a variable position valve operated by a
stepper motor. The ETV is located in the suction
line between the accumulator and the suction
vibrasorber. The ETV system also uses discharge
and suction pressure transducers, and a hot gas
bypass valve.
The ETV has two internal coils. The
microprocessor operates the valve by energizing
the coils with a variable frequency ac signal. The
valve position can be monitored with the
G
AUGES
key. Zero (0) indicates the valve is fully
closed and 800 indicates the valve is fully open.
The microprocessor tests the ETV if required
when the unit is started. Alarm Code 89 indicates
the refrigeration system pressures did not respond
as expected during the test. This may be caused by
a malfunction of the ETV or by a refrigeration
system problem such as low refrigerant level, a
frozen expansion valve, or a restriction in suction
line. The microprocessor ignores the test results if
the box temperature or the ambient temperature is
below 10 F (-12 C). The ETV test can also be
performed using the Service Test Mode.
Use the
G
AUGES
key to observe of the ETV
position during the ETV test. The expected ETV
position observation is a decrease followed by an
increase. The suction pressure should decrease
when the valve position decreases and increase
when the valve position increases.
Refer to the SR-4 Microprocessor Control System
Diagnostic Manual TK 55533 for complete
information about the testing and operation of the
ETV.
See “Electronic Throttling Valve” in the
Refrigeration Service Operations chapter of this
manual for removal and installation procedures.
Pressure Transducers
The discharge pressure transducer and the suction
pressure transducer supply pressure information
to the microprocessor. These pressures can be
monitored with the
G
AUGES
key. Check the
readings by comparing them to the readings on a
gauge manifold set attached to the compressor.
Refer to the SR-4 Microprocessor Control System
Diagnostic Manual TK 55533 for more
information about the testing and operation of the
pressure transducers.
Hot Gas Bypass Valve
The hot gas bypass valve is used in conjunction
with the electronic throttling valve to reduce the
capacity of the unit during modulation. This
normally closed solenoid valve is located in the
refrigeration line that connects the discharge line
to the hot gas line. The hot gas bypass valve is
energized (opened) at full modulation. The hot
gas bypass valve is de-energized (closed) when
modulation is discontinued.
Refer to the SR-4 Microprocessor Control System
Diagnostic Manual TK 55533 for information
about testing the hot gas solenoid. See the
Refrigeration Service Operations chapter of this
manual for removal and installation procedures.
1.
Inlet
2.
Valve Body
3.
Stepper Motor
4.
Outlet
Figure 214: Electronic Throttling Valve
2
3
4
1
