SERVICING
45 Rev 1
S-109 CHECKING SUBCOOLING
Refrigerant liquid is considered subcooled when its tem-
perature is lower than the saturation temperature corre-
sponding 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 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. Convert the liquid line pressure gauge reading to tem-
perature by finding the gauge reading in Temperature -
Pressure Chart and reading to the left, find the tempera-
ture in the °F column.
5. The difference between the thermometer reading and
pressure to temperature conversion is the amount of
subcooling.
EXAMPLE:
a. Liquid Line Pressure = 260
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. The normal subcooling
range is 9° - 13° subcooling for heat pumps units, 14 to 18
for straight cool units.
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, evacu-
ate and recharge.
S-111 CAPILLARY TUBES/RESTRICTOR ORI-
FICES
The capillary tubes/restrictor orifices used in conjunction
with the indoor and outdoor coil, are a predetermined length
and bore (I.D.).
They are designed to control the rate of liquid refrigerant flow
into an evaporator coil.
The amount of refrigerant that flows through the capillary
tube/restrictor orifice 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 decrease, causing less refrigerant flow.
A strainer is placed on the entering side of the tubes to
prevent any foreign material from becoming lodged inside
the capillary tubes.
If a restriction should become evident, proceed as follows:
1. Capture the refrigerant charge.
2. Remove the capillary tubes/restrictor orifice or tube
strainer assembly. and replace.
3. Replace liquid line drier, evacuate and recharge.
Capillary Tubes/Orifice Assembly
CHECKING EQUALIZATION TIME
During the "OFF" cycle, the high side pressure bleeds to the
low side through the capillary tubes/restrictor orifices. 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 the capillary tubes/
restrictor orifices are inoperative. Replace, install a liquid
line drier, evacuate and recharge.
Aerqouip Flow Control Assembly
