Field Charging Procedures - Fedders C1018BBD Installation, Operation And Maintenance Manual

FIELD CHARGING PROCEDURES

SUPERHEAT CHARGING
The superheat method is highly recommended for field charging or
checking the existing refrigerant charge in a system. Because each
installation is different in terms of indoor air flow, refrigerant line
length, duct variations, etc., the factory charge may not be correct
for every application. To assure the best performance from the air
conditioner, the refrigerant charge should be checked and adjusted
when needed on each installation.
For proper superheat readings, a standard low side refrigerant
gauge and an accurate thermometer are needed. A mercury or stem
type thermometer is not adequate for suction line temperatures. We
recommend electronic thermocouple thermometers (available at
most refrigeration wholesalers); however, an accurate remote bulb
thermometer can be used. When measuring the line temperature,
be sure the thermometer is well-insulated to assure accurate
measurements. The chart on page 7 gives superheat values at
various outdoor temperatures. Allow at least 5 minutes running time
between charge adjustment for the unit to stabilize.
Chart on page 7 is based on 360 to 400 CFM/ton indoor airflow and
50% relative humidity. Use on systems that cool with fixed restrictor.
SUCTION PRESSURE is 65 PSI which equals 38°F / 3.3°C on the
R-22 scale of the low side gauge.
SUCTION LINE temperature taken at the unit is 70°F / 21.1°C.
70°F / 21.1°C minus 38°F / 3.3°C equals 32°F / 17.8°C superheat.
SUBCOOLING CHARGING
The subcooling charging method is to be used on units which have
Thermostatic Expansion Valves (TXV) as the expansion device.
For proper subcooling readings, a standard high side gauge is
required for pressure readings.
Use the chart on page 7 to determine the required subcooling value.
INSTRUCTIONS
1. Measure the outdoor air temperature. (T1)
2. Measure the liquid line pressure at the outdoor unit and
determine condenser refrigerant temperature by the scale
on the high side pressure gauge. (T2)
(for units with pistons)
(for units with TXVs)
OUTDOOR TEMPERATURE is 90°F / 32.2°C, indoor temperature is
80°F / 26.7°C.
INTERSECTION of the indoor temperature and outdoor
temperature lines occurs on the 12°F / 6.7°C superheat line.
ADD CHARGE to obtain 12°F / 6.7°C superheat.
INSTRUCTIONS
1. Measure suction pressure and determine evaporator
refrigerant temperature on R-22 scale of low side gauge.
2. Measure suction line temperature on suction line at the
outdoor unit.
3. Measure outdoor and indoor temperature.
4. Determine from the table what the superheat should be,
considering the indoor and outdoor ambient temperatures.
(Example indicates 12°F / 6.7°C superheat.)
5. Adjust charge if needed. Be sure unit is running at stabilized
condition.
NOTE:
If operating superheat is more than 5°F / 2.8°C above the
chart value, add refrigerant. If below the chart value, remove
refrigerant. If below the limit line, remove refrigerant. When
removing refrigerant, always be certain to use standard reclaim
procedures.
3. Measure the liquid line temperature on the liquid line at the
outdoor unit. (T3)
4. Subtract T3 from T2. (T2 – T3) This is the subcooling value.
Compare this value and the outdoor temperature (T1), to the
charts on page 7. If the value is below the line, add
refrigerant. If the value is above the line, remove refrigerant
charge.
NOTE:
When removing refrigerant, always use standard reclaim
procedures.
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