Southbend 20108RSB - Manual (Page 11)

CORRECTIVE MAINTENANCE
11 Printed in USA 12/02 Refrigerated Base-Remote © 2002
If the system overcharge is sufficient enough to immerse the
major parts of a hermetic compressor in liquid refrigerant, a
situation has been created that when followed by unusual but
possible circumstances, can lead to compressor housing
seam separation or rupture.
The sequence of circumstances that can lead to compressor
housing seam separation or rupture occurs in the following
manner:
1. The system overcharge immerses the compressor
motor, piston, connecting rods, cylinders, etc. in liquid
refrigerant, thereby effectively forming a hydraulic block
preventing the compressor from starting. This
condition is known as locked rotor.
2. Electrical current continues to flow through the
compressor motor windings that become, in effect,
electric resistance heaters. The heat produced begins
to vaporize the excessive liquid overcharge, causing a
rapid increase in system pressure.
3. If the system compressor protective devices fail for any
reason prior to or during this locked rotor heating cycle
or cycles, liquid refrigerant may be vaporized
sufficiently fast enough to raise the pressure within the
system to extremes far greater that the housing or weld
seam is designed to handle.
4. In some instances where the amount of refrigerant
overcharge is critical in proportion to the system
internal volume, the pressure reached can cause a
compressor housing seam separation or rupture that
can be hazardous.
The remedy to eliminate this exceedingly rare, but potential
hazard is to use correct refrigerant charge amounts and
techniques.
Middleby urges that all individuals responsible for training,
teaching, or advising installation mechanics and service
personnel emphasize proper charging techniques. In
addition, Middleby advises strict adherence to refrigerant
charge amounts specifically recommended by the
manufacturer of the refrigeration, air conditioning, or heat
pump system.
Replacement of Low Pressure Control
1. Disconnect the unit from electrical service.
2. Remove control cover and disconnect electrical
terminals.
3. Disconnect capillary tube.
4. Remove mounting fasteners on control base and install
new control by reversing the procedure.
5. To adjust the control, hook up the service gauges to
the suction and discharge valves and crack them to
allow the gauges to read.
6. Using a standard screwdriver, coarse adjust the control
by turning the adjustment screws on top of the control.
Preset the cut-in and cutout and 68 lbs. and 38 lbs.
respectively for a refrigerator and 25 lbs. and 10 lbs.
respectively for a freezer.
7. Start the system. Allow it to run for five minutes.
Monitor the low side pressure. Fine adjustments will
be required to achieve the prescribed cycling
pressures.
NOTE: Running the suction valve in or out as required to
effectively change the pressures can speed up the control
adjustment process.
Replacement of Thermal Expansion Valve (TXV)
1. Close liquid valve and run compressor until it pumps
refrigerant into the receiver (low side service gauge will
read 1 lbs.). Close the suction line valve.
2. Disconnect the sensor bulb on the suction line.
3. Disconnect the liquid line (1/4") and suction line (3/8")
then remove the TXV.
4. Install new TXV, reconnect lines, and re-fasten the
sensor bulb.
NOTE: It is not recommended to adjust the valve super heat
as this comes pre-set from the factory.
Replacement of Filter Dryer i
1. Close liquid line valve and run compressor until the low
side refrigeration gauge indicates zero lbs., then close
suction.
2. Remove filter dryer from system and replace with new
dryer.
3. Purge system and add refrigerant if needed.
Replacement of Condenser Fan Motor i
1. Disconnect all electrical power to the unit.
2. Remove the condensing unit from the condensing unit
compartment.
3. Remove the protective wire shroud from around the
motor.
4. Disconnect the fan motor leads from the terminal box
on the compressor.
5. Remove the mounting screws at the motor base.
6. Using an allen wrench, remove the aluminum fan.
7. To install the new motor, reverse the process.