Service Instructions

SERVICING
118
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
Temperature - 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
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 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, 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 appear-
ance of an undercharged unit. However, the unit will have normal
to high subcooling.
Locate the restriction, replace the restricted part, replace drier,
evacuate and recharge.
S-113 OVERCHARGE OF REFRIGERANT
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 capillary tube metering device, could
allow refrigerant to return to the compressor under extreme
overcharge conditions. Also with a capillary tube 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 gas from the suction
line dill valve 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 system
contains non-condensables.
S-114 NON-CONDENSABLES
If non-condensables are suspected, shut down the system and
allow the pressures to equalize. Wait at least 15 minutes.
Compare the pressure to the temperature of the coldest coil since
this is where most of the refrigerant will be. If the pressure
indicates a higher temperature than that of the coil temperature,
non-condensables are present.
Non-condensables are removed from the system by first remov-
ing the refrigerant charge, replacing and/or installing liquid line
drier, evacuating and recharging.
CHECKING COMPRESSOR EFFICIENCY
The reason for compressor inefficiency is broken or damaged
scroll flanks on Scroll compressors, reducing the ability of the
compressor to pump refrigerant vapor. The condition of the
scroll flanks is checked in the following manner.
1. Attach gauges to the high and low side of the system.
2. Start the system and run a “Cooling Performance Test. If the
test shows:
a. Below normal high side pressure.
b. Above normal low side pressure.
c. Low temperature difference across coil.
d. Low amp draw at compressor.
And the charge is correct. The compressor is faulty –
replace the compressor.