43
Compare calculated superheat to the
acceptable cooling mode superheat values
between 4.4 and 8.3°C (8 - 15°F) for all
system types. Superheat will increase with
long suction line runs.
For refrigeration systems with tandem
compressors, it is critical that the suction
superheat setpoint on the TXV is set with one
compressor running. The suction superheat
must be between 5.6 and 7.2
°
C (10-13°F)
with one compressor running. The suction
superheat
will
increase
with
both
compressors in a tandem running. Inadequate
suction superheat can allow liquid refrigerant
to return to the compressors which will wash
the oil out of the compressor. Lack of oil
lubrication will destroy a compressor.
Measure liquid sub-cooling with both
compressors in a refrigeration system
running.
Adjusting
Sub-Cooling
and
Superheat
Temperatures
The system is overcharged if the sub-cooling
temperature is too high and the evaporator is
fully loaded (low loads on the evaporator
result in increased sub-cooling) and the
evaporator
superheat
is
within
the
temperature range as shown in the table
above (high superheat results in increased
sub-cooling).
Correct an overcharged system by reducing
the amount of refrigerant in the system to
lower the sub-cooling.
The system is undercharged if the superheat
is too high and the sub-cooling is too low.
Correct an undercharged system by adding
refrigerant to the system to reduce superheat
and raise sub-cooling.
If the sub-cooling is correct and the superheat
is too high, the TXV may need adjustment to
correct the superheat. Before adjusting the
TXV, verify the sensing bulb is in the correct
position according to Figure 23 and follow
the guidelines below.
1. The suction line is clean where the sensing
bulb is attached.
2. The entire length of the sensing bulb is in
contact with the suction line.
3. Place the sensing bulb several centimeters
(inches) downstream of the equalizer line.
4. The sensing bulb is fully insulated.
5. If the sensing bulb is installed on a vertical
portion of the suction line, place the sensing
bulb upstream of suction line trap.
Thermal expansion valve must be
adjusted between 4.4 and 8.3
°
C
(8-15°F) of suction superheat. Failure
to have sufficient superheat will
damage the compressor and void the
warranty.
CAUTION
DO NOT OVERCHARGE!
Refrigerant overcharging leads to
excess refrigerant in the condenser
coils resulting in elevated compressor
discharge pressure.
CAUTION