72
SERVICING
4. Disconnect manifold set. Installation is complete.
S-109 CHECKING SUBCOOLING
Refrigerant liquid is considered subcooled when its tempera
-
ture is lower than the saturation temperature corresponding to
its pressure. The degree of subcooling equals the degrees of
temperature decrease below the saturation temperature at the
existing pressure.
1. Attach an accurate thermometer or preferably a thermocou
-
ple type temperature tester to the liquid line as it leaves the
condensing unit.
2. Install a high side pressure gauge on the high side (liquid)
service valve at the front of the unit.
3. Record the gauge pressure and the temperature of the line.
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 108). 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 Tem
-
perature - Pressure Chart and reading to the left, find the
temperature in the °F. Column.
6. The difference between the thermometer reading and pres
-
sure to temperature conversion is the amount of subcooling.
Add charge to raise subcooling. Recover charge to lower sub
-
cooling.
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 refrig
-
erant 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. For best results, temporarily install a thermometer on the
liquid line at the liquid line service valve and 4-6” from the
compressor on the suction line. Ensure the thermometer
makes adequate contact and is insulated for best possible
readings. Use liquid line temperature to determine sub-cool
-
ing and vapor temperature to determine superheat.
NOTE
: An optional method is to locate the thermometer
at the suction line service valve. Ensure the thermometer
makes adequate contact and is insulated for best possible
readings.
3. Check subcooling and superheat. Systems with TXV applica
-
tion should have a subcooling of 7 to 9 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 7 to 9 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 7 to 9 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 tempera
-
ture will fall.
4. If a temperature or pressure change is noticed, the expan
-
sion 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 conjunction
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.
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