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7
LOW-CHARGE COOLING
Using Cooling Charging Charts (Fig. 10-14.), vary refrigerant
until the conditions of the appropriate chart are met. Note the
charging charts are different from the type normally used.
Charts are based on charging the units to the correct subcooling
for the various operating conditions. Accurate pressure gage
and temperature sensing device are required. Connect the pres-
sure gage to the service port on the discharge line. Mount the
temperature sensing device on the liquid line leaving the con-
denser coil and insulate it so that outdoor ambient temperature
does not affect the reading. Indoor-air cfm must be within the
normal operating range of the unit.
TO USE COOLING CHARGING CHARTS
Select the appropriate unit charging chart from Fig. 10-14.
Take the liquid-line temperature and read the discharge pres-
sure gage. Refer to chart to determine what liquid-line tem-
perature should be. If liquid-line temperature is high, add re-
frigerant. If liquid-line temperature is low, carefully recover
some of the charge. Recheck the discharge pressure as charge
is adjusted.
Evacuation
Proper evacuation of the system will remove non-condensables
and ensure a tight, dry system before charging. Evacuate from
both high and low side ports. Never use the system compressor
as a vacuum pump. Refrigerant tubes and indoor coil should be
evacuated to 500 microns. Always break a vacuum with dry ni-
trogen. The two possible methods are the deep vacuum method
and the triple evacuation method.
DEEP VACUUM METHOD
The deep vacuum method requires a vacuum pump capable of
pulling a minimum vacuum of 500 microns and a vacuum gage
capable of accurately measuring this vacuum depth. The deep
vacuum method is the most positive way of assuring a system
is free of air and liquid water. (See Fig. 9.)
Fig. 9 — Deep Vacuum Graph
TRIPLE EVACUATION METHOD
The triple evacuation method should only be used when vacu-
um pump is capable of pumping down to 28-in. of mercury and
system does not contain any liquid water.
Proceed as follows:
1. Pump system down to 28-in. of mercury and allow pump
to continue operating for an additional 15 minutes.
2. Close service valves and shut off vacuum pump.
3. Connect a nitrogen cylinder and regulator to system and
open until system pressure is 2 psig.
4. Close service valve and allow system to stand for 1 hour.
During this time, dry nitrogen will be able to diffuse
throughout the system, absorbing moisture.
5. Repeat this procedure. System will then contain minimal
amounts of contaminants and water vapor.
LEAK IN
S
Y
S
TEM
VACUUM TIGHT
TOO WET
TIGHT
DRY
S
Y
S
TEM
0
1
2
3
4
5
6
7
MINUTE
S
5000
4500
4000
3
500
3
000
2500
2000
1500
1000
500
MICRON
S
Summary of Contents for 50LC 14
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