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SERVICING
2. Install a high side pressure gauge on the liquid access
fitting.
3. Record the gauge pressure and the temperature of the line.
4. Compare the hi-pressure reading to the "Required Liquid
Line Temperature" chart. 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.
5. The difference between the thermometer reading and pres-
sure to temperature conversion is the amount of 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.
See R410A Pressure vs. Temperature chart.
S-111 FIXED ORIFICE RESTRICTION
DEVICES
The fixed orifice restriction 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
restriction device is regulated by the pressure difference be-
tween 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, increas-
ing 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.
If a restriction should become evident, proceed as follows:
1. Recover refrigerant charge.
2. Remove the orifice assembly and clean or replace.
3. Replace liquid line drier, evacuate and recharge.
36
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 restric-
tion device is inoperative. Replace, install a liquid line drier,
evacuate and recharge.
S-112 CHECKING RESTRICTED LIQUID LINE
When the system is operating, the liquid line is warm to the
touch. If the liquid line is restricted, a definite temperature
drop will be noticed at the point of restriction. In severe cases,
frost will form at the restriction and extend down the line in the
direction of the flow.
Discharge and suction pressures will be low, giving the ap-
pearance of an undercharged unit. However, the unit will have
normal to high subcooling.
If a restriction is located, replace the restricted part, replace
drier, evacuate and recharge.
S-113 REFRIGERANT OVERCHARGE
An overcharge of refrigerant is normally indicated by an exces-
sively high head pressure.
An evaporator coil, using an expansion valve metering device,
will basically modulate and control a flooded evaporator and
prevent liquid return to the compressor.
An evaporator coil, using a fixed orifice restrictor device
(flowrator) metering device, could allow liquid refrigerant to re-
turn to the compressor under extreme overcharge conditions.
Also with a fixed orifice restrictor device (flowrator) metering
device, extreme cases of insufficient indoor air can cause icing
of the indoor coil and liquid return to the compressor, but the
head pressure would be lower.
There are other causes for high head pressure which may be
found in the "Service Problem Analysis Guide."
If other causes check out normal, an overcharge or a system
containing non-condensables would be indicated.
If this system is observed:
1. Start the system.
2. Remove and capture small quantities of refrigerant as from
the suction line access fitting until the head pressure is
reduced to normal.
3. Observe the system while running a cooling performance
test. If a shortage of refrigerant is indicated, then the sys-
tem contains non-condensables.
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