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SERVICING
67
4. Review the technical information manual or specification
sheet for the model being serviced to obtain the design
subcooling.
5. Compare the hi-pressure reading to the "Required Liquid
Line Temperature" chart (page 43). Find the hi-pressure
value on the left column. Follow that line right to the
column under the design subcooling value. Where the two
intersect is the required liquid line temperature.
Alternately you can convert the liquid line pressure gauge
reading to temperature by finding the gauge reading in
Temperature - Pressure Chart and reading to the left, find
the temperature in the °F. Column.
6. The difference between the thermometer reading and
pressure to temperature conversion is the amount of
subcooling.
Add charge to raise subcooling. Recover charge to lower
subcooling.
Subcooling Formula = Sat. Liquid Temp. - Liquid Line
Temp.
EXAMPLE:
a. Liquid Line Pressure = 417
b. Corresponding Temp. °F. = 120°
c. Thermometer on Liquid line = 109°F.
To obtain the amount of subcooling subtract 109°F from
120°F.
The difference is 11° subcooling. See the specification sheet
or technical information manual for the design subcooling
range for your unit.
S-109A TWO SPEED APPLICATION
Run the remote on low stage cooling for 10 minutes until
refrigerant pressures stabilize. Follow the guidelines and
methods below to check unit operation and ensure that the
refrigerant charge is within limits. Charge the unit on low
stage.
1. Purge gauge lines. Connect service gauge manifold to
base-valve service ports. Run system at least 10 minutes
to allow pressure to stabilize.
2. Temporarily install thermometer on liquid (small) line
near liquid line service valve with adequate contact and
insulate for best possible reading.
3. Check subcooling and superheat. Systems with TXV
application should have a subcooling of 5 to 7 ºF and
superheat of 7 to 9 ºF.
a. If subcooling and superheat are low, adjust TXV to
7 to 9 ºF superheat, then check subcooling.
NOTE: To adjust superheat, turn the valve stem
clockwise to increase and counter clockwise to
decrease.
b. If subcooling is low and superheat is high, add
charge to raise subcooling to 5 to 7 ºF then check
superheat.
c. If subcooling and superheat are high, adjust TXV
valve to 7 to 9 ºF superheat, then check subcooling.
d. If subcooling is high and superheat is low, adjust
TXV valve to 7 to 9 ºF superheat and remove
charge to lower the subcooling to 5 to 7 ºF.
NOTE: Do NOT adjust the charge based on suction
pressure unless there is a gross undercharge.
4. Disconnect manifold set, installation is complete.
Subcooling Formula = Sat. Liquid Temp. - Liquid Line Temp.
S-110 CHECKING EXPANSION VALVE
OPERATION
1. Remove the remote bulb of the expansion valve from the
suction line.
2. Start the system and cool the bulb in a container of ice
water, closing the valve. As you cool the bulb, the suction
pressure should fall and the suction temperature will rise.
3. Next warm the bulb in your hand. As you warm the bulb,
the suction pressure should rise and the suction tem-
perature will fall.
4. If a temperature or pressure change is noticed, the
expansion valve is operating. If no change is noticed, the
valve is restricted, the power element is faulty, or the
equalizer tube is plugged.
5. Capture the charge, replace the valve and drier, evacuate
and recharge.
S-111 FIXED ORIFICE RESTRICTOR DEVICES
The fixed orifice restrictor device (flowrator) used in conjunc-
tion with the indoor coil is a predetermined bore (I.D.).
It is designed to control the rate of liquid refrigerant flow into
an evaporator coil.
The amount of refrigerant that flows through the fixed orifice
restrictor device is regulated by the pressure difference
between the high and low sides of the system.
In the cooling cycle when the outdoor air temperature rises,
the high side condensing pressure rises. At the same time,
the cooling load on the indoor coil increases, causing the low
side pressure to rise, but at a slower rate.
Since the high side pressure rises faster when the tempera-
ture increases, more refrigerant flows to the evaporator,
increasing the cooling capacity of the system.
When the outdoor temperature falls, the reverse takes place.
The condensing pressure falls, and the cooling loads on the
indoor coil decreases, causing less refrigerant flow.
A strainer is placed on the entering side of the tube to prevent
any foreign material from becoming lodged inside the fixed
orifice restriction device.
If a restriction should become evident, proceed as follows:
1. Recover refrigerant charge.