SERVICING
49
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 thermo-
couple 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.
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 OPERA-
TION
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 and
evacuate.
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.
2. Remove the orifice or tube strainer assembly and re-
place.
3. Replace liquid line drier, evacuate and recharge.
CHECKING EQUALIZATION TIME
During the "OFF" cycle, the high side pressure bleeds to the
low side through the fixed orifice restriction device. Check
equalization time as follows:
1. Attach a gauge manifold to the suction and liquid line dill
valves.
2. Start the system and allow the pressures to stabilize.
3. Stop the system and check the time it takes for the high
and low pressure gauge readings to equalize.
If it takes more than seven (7) minutes to equalize, the
restrictor device is inoperative. Replace, install a liquid line
drier, evacuate and recharge.
