AAON LZ Series, Установка, эксплуатация и обслуживание

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54
Checking Liquid Sub-cooling
Measure the temperature of the liquid line as
it leaves the condenser coil.
Read the gauge pressure at the liquid line
close to the point where the temperature was
taken. You must use liquid line pressure as it
will vary from discharge pressure due to
condenser coil pressure drop.
Convert the pressure obtained to a saturated
temperature using the appropriate refrigerant
temperature-pressure chart.
Subtract the measured liquid line temperature
from the saturated temperature to determine
the liquid sub-cooling.
Compare calculated sub-cooling to the table
below for the appropriate unit type and
options.
Verify the liquid pressure and temperature
readouts before considering the sub-cooling
reading valid.
Checking Evaporator Superheat
Measure the temperature of the suction line
close to the compressor.
Read gauge pressure at the suction line close
to the compressor.
Convert the pressure obtained to a saturated
temperature using the appropriate refrigerant
temperature-pressure chart.
Subtract the saturated temperature from the
measured suction line temperature to
determine the evaporator superheat.
The suction superheat should be 10-15°F
with one compressor 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. Liquid
sub-cooling should be measured with both
compressors in a refrigeration system
running.
Compare calculated superheat to Table 12 for
the appropriate unit type and options.
Table 12 - Acceptable Refrigeration Circuit
Values
Air-Cooled Condenser with Scroll
Compressors
Sub-Cooling 7-12°F
Superheat 10-15°F
Evaporative-Condensed Chiller with
Scroll Compressors
Sub-Cooling 6-10°F
Superheat 10-15°F
Adjusting Sub-cooling 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 Table 12 (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.
DO NOT OVERCHARGE!
Refrigerant overcharging leads to
excess refrigerant in the condenser
coils resulting in elevated compressor
discharge pressure.
CAUTION