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Maintenance
5. If using flux, apply it sparingly to the joint. Excess flux
will contaminate the refrigerant system.
6. Apply heat evenly over the length and circumference
of the joint.
7. Begin brazing when the joint is hot enough to melt the
brazing rod. The hot copper tubing, not the flame,
should melt the rod.
8. Continue to apply heat evenly around the joint
circumference until the brazing material is drawn into
the joint by capillary action, making a mechanically
sound and gas-tight connection.
9. Visually inspect the connection after brazing to locate
any pinholes or crevices in the joint. Use a mirror if
joint locations are difficult to see.
System Evacuation Procedures
•
Each refrigeration circuit must be evacuated before the
unit can be charged and started.
•
Use a rotary type vacuum pump capable of pulling a
vacuum of 100 microns or less.
•
Verify that the unit disconnect switch and the system
control circuit switches are "OFF".
•
Oil in the vacuum pump should be changed each time
the pump is used with high quality vacuum pump oil.
Before using any oil, check the oil container for
discoloration, which usually indicates moisture in the
oil and/or water droplets. Moisture in the oil adds to
what the pump has to remove from the system, making
the pump inefficient.
•
When connecting vacuum pump to refrigeration
system, it is important to manifold vacuum pump to
both high and low side of system (liquid line access
valve and suction line access valve). Follow pump
manufacturer's directions for proper methods of using
vacuum pump.
•
Lines used to connect the pump to the system should
be copper and of the largest diameter that can
practically be used. Using larger line sizes with
minimum flow resistance can significantly reduce
evacuation time.
•
Rubber or synthetic hoses are not recommended for
system evacuation. They have moisture absorbing
characteristics that result in excessive rates of
evaporation, causing pressure rise during standing
vacuum test. This makes it impossible to determine if
system has a leak, excessive residual moisture, or
continual or high rate of pressure increase due to
hoses.
•
Install an electronic micron vacuum gauge in the
common line ahead of the vacuum pump shutoff valve,
as shown in
Figure 48, p.
and open Valve A.
•
Start vacuum pump. After several minutes the gauge
reading will indicate the maximum vacuum the pump
64
65. 94. Close Valves B and C,
is capable of pulling. Rotary pumps should produce
vacuums of 100 microns or less.
NOTICE
Motor Winding Damage!
Failure to follow instructions below could result in
compressor motor winding damage. Do not use a
megohm meter or apply voltage greater than 50 VDC to
a compressor motor winding while it is under a deep
vacuum.
•
Open Valves B and C. Evacuate system to a pressure of
300 microns or less. As vacuum is being pulled on
system, it may appear that no further vacuum is being
obtained, yet pressure is high. It is recommended
during evacuation process to "break" vacuum to
facilitate evacuation.
•
To break the vacuum, shut valves A, B, & C and connect
a refrigerant cylinder to charging port on manifold.
Purge air from hose. Raise standing vacuum pressure
in system to "zero" (0 psig) gauge pressure. Repeat
process two or three times during evacuation.
Note: It is unlawful to release refrigerant into the
atmosphere. When service procedures require
working with refrigerants, the service technician
must comply with all Federal, State, and local laws.
Standing Vacuum Test
Once 300 microns or less is obtained, close valve A and
leave valves B and C open to allow the vacuum gauge to
read the actual system pressure. Let system equalize for
approximately 15 minutes. This is referred to as a
"standing vacuum test" where time versus pressure rise.
Maximum allowable rise over a 15 minute period is 200
microns. If pressure rise is greater than 200 microns but
levels off to a constant value, excessive moisture is
present. If pressure steadily continues to rise, a leak is
indicated.
Figure 49, p. 65
of "standing vacuum test".
If a leak is encountered, repair the system and repeat the
evacuation process until the recommended vacuum is
obtained. Once the system has been evacuated, break the
vacuum with refrigerant and complete the remaining Pre-
Start procedures before starting the unit.
illustrates three possible results
PKG-SVX027A-EN
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