Thermo King SB-210, Manual

Page: 107 / 159

Refrigeration Maintenance
107
8. The gauges will remain in this position,
approximately zero, if the three-way valve
seals properly toward the condenser and the
condenser pressure bypass check valve seals
properly.
9. Back seat condenser pressure bypass check
valve stem against the snap ring. Both gauges
should rise indicating the condenser pressure
bypass check valve is properly releasing
condenser pressure into the discharge tube and
evaporator.
10. Replace the cap on the condenser pressure
bypass check valve.
NOTE: Valve stem MUST be back seated
during normal unit operation.
11. Open the receiver tank return outlet valve,
remove the gauges and return the unit to
normal operation.
Electronic Throttling Valve
(ETV)
The Electronic Throttling Valve (ETV) is optional
on the SB-210 30. It is standard on the SB-210 50
and SB-310 30.
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 evaporator and the heat exchanger.
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
AUGE
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
AUGE
key to check the operation of the
ETV during the ETV test. The valve position
should be 0 at the start of the test when the valve
is fully closed, and should go to a higher value
when the valve is opened. The suction pressure
should decrease while the valve is fully closed,
and should begin to increase when the valve is
opened.
Refer to the SR-2 Microprocessor Control System
Diagnostic Manual TK 51587 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
AUGE
key. Check the readings
by comparing them to the readings on a gauge
manifold set attached to the compressor. Refer to
the SR-2 Microprocessor Control System
Diagnostic Manual TK 51587 for more
information about the testing and operation of the
pressure transducers.
1. Outlet
2. Stepper Motor
3. Valve Body
4. Inlet
Figure 94: Electronic Throttling Valve
ARD078
2
3
1
4