EVACUATE THE SYSTEM
CyberAiR DX Floor Mounted IOM Manual
Table 3:
Weight of R-410A Refrigerant
(Lbs./100Ft of Type L Tubing)
Line Size
O.D.
Liquid
Line
Discharge
Line
1/2
5.88
1.27
5/8
9.44
2.03
7/8
19.62
4.22
1 1/8
33.44
7.20
1 3/8
50.95
10.97
1 5/8
72.11
15.53
2 1/8
158.29
34.09
Example:
Estimate the amount of R-410A
refrigerant required for each compressor circuit in a
system consisting of a 10 ton (CFD-035-D2A) A/C
unit, connected with a 1/2” x 30 foot liquid line and
7/8” x 30 foot discharge line to a STULZ Model
SCS-252-DSA dual circuit condenser.
Circuit 1
+ A/C Unit (Circuit 1)
=
2.7 lbs
+ 1/2” Liquid Line: 30 x 5.88
=
1.764 lbs
100
+ 7/8” Discharge Line: 30 x 4.22 =
1.266 lbs
100
+ Condenser
=
3.2 lbs
Estimated Refrigerant Charge =
8.93 lbs
(Round off to nearest lb = 9.0
lbs)
Circuit 2
+ A/C Unit (Circuit 2)
=
2.7 lbs
+ 1/2” Liquid Line: 30 x 5.88
=
1.764 lbs
100
+ 7/8” Discharge Line: 30 x 4.22 =
1.266 lbs
100
+ Condenser
=
3.2 lbs
Estimated Refrigerant Charge =
8.93 lbs
(Round off to nearest lb = 9.0
lbs)
2.9.4 Preparing System For Charging
1. With all the system piping connections made,
perform a dry nitrogen leak detection test on the
system. Using dry nitrogen only, pressurize the
system to 150 psig. Ensure all service and
solenoid valves are energized open and that no
part of the system is isolated from the
pressurized nitrogen.
2. Since there is no refrigerant in the system to
detect at this point, leaks may be detected by
observing
if there’s been a change in the standing
pressure after 12 hours. A significant drop in
pressure (>10 psig) indicates a leak in the
system that needs to be repaired. After the
system is determined to be free of leaks, you
may evacuate the system.
CAUTION
A proper vacuum must be drawn on the
refrigerant system to remove moisture prior to
charging. If this is not done the refrigerant
charge will combine with moisture in the pipes
to form an acid that will eventually lead to
compressor failure. A triple evacuation
procedure with dry nitrogen is recommended
especially for systems with newly installed
refrigerant piping.
NOTE
A vacuum pump should be used that is
capable of evacuating the entire volume of
the A/C system, including newly installed or
existing piping. It is essential to use a well
maintained pump that is in good operating
condition. Always ensure it contains clean,
fresh oil. Manufacturers recommend you
change the oil in the pump regularly to
maintain its ability to remove moisture.
NOTE
Use high quality hoses ensuring they are free
of defects and don’t leak. It is recommended to
use copper tubing instead of hoses if possible
due to the low vacuum that must be attained
when evacuating the system. The use of
short, large diameter hoses helps reduce
evacuation time.
3. After ensuring there are no leaks, relieve
pressure and evacuate the entire system while
maintaining all the solenoids open. Pull an initial
vacuum of 1500 microns or lower using the
suction and discharge service ports.
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