Sears GR-151SPF - Manual (Page 2)

In case that a considerable leakage occurs and to stop the
vacuum pump will be necessary and add a small quantity
of Freon to the system, if vacuum should not be obtained
(pressure gauge can't fall to 1 atmosphere.), start the
refrigeration unit and find the leakage with the special
leak-finder. When the defective soldering point is visible,
re-do it after opening the extension tube valve and
reestablishing the normal outside pressure inside the
group.
Because the melted alloy is sucked into the tubes and
block them, the pressure must be rebalanced when
vacuum is in the system in soldering. As soon as the
vacuum operation is over, add the quantity in grams of R-
12 to the refrigeration system. Remember that every
system has an exact quantity of R-12 with a tolerance of
±5 grams than can be added. (Figure 5)
Figure 5
Before performing this operation (if the vacuum pump and
refilling cylinder are connected), make sure that the valve
placed between the vacuum pump and refilling tube are
closed to keep the Freon for adding to the system. (Figure 6)
In addition, check the graduated scale on the cylinder for
the quantity of R-12 to be added, for example, if we have
750 grams of Freon in the cylinder and must add 165
grams to the group, this amount will be reached when R-12
has dropped to 585 grams, remembering that the indicator
shows a lower limit of meniscus. Do this after choosing the
scale corresponding to the gas pressure different scales
reported as the same gas pressure indicated by the
pressure gauge on the top of the column.
To make R-12 flow into the system, open the valve placed
at the base of the cylinder and connected to the filling tube.
The amount of Freon cannot be added to the system all at
once because it may cause a blocking of motor-compressor.
Therefore, proceed by adding original quantity of about
20-30 grams and close the valve immediately.
The pressure rises and the motor-compressor must start,
sucking the gas and making the pressure go down again.
Regulate the valve again, maintaining the same manner
until reaching the quantity of R-12 established for the
system being charged. When the system is running, the
suction pressure must be stabilized from 0.30 to 0.6
atmosphere.
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