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SERVICING
The TXV should NOT be adjusted at light load conditions
55º to 60ºF, under such conditions only the subcooling
can be evaluated. This is because suction pressure is
dependent on the indoor coil match, indoor airflow, and
wet bulb temperature.
NOTE: Do NOT adjust charge based on suction pressure
unless there is a gross undercharge.
4. Disconnect manifold set. Installation is complete.
S-109 Checking Subcooling
Refrigerant liquid is considered subcooled when its
temperature 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
thermocouple type temperature tester to the liquid
line close to the pressure switch.
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. Compare the hi-pressure reading to the "Required
Liquid Line Temperature" chart on the following
page. 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.
5. 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.
24
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-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
temperature 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 and
evacuate.
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.
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
temperature 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.
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