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Mechanical Installation
Table 7: Pressure-Vacuum Equivalents
Absolute pressure above zero
Microns
PSIA
0
0
50
0.001
100
0.002
150
0.003
200
0.004
300
0.006
500
0.009
1,000
0.019
2000
0.039
4,000
0.078
6000
0.117
8,000
0.156
10,000
0.193
15,000
0.290
20,000
0.387
30,000
0.580
50,000
0.967
100,000
1.930
200,000
3.870
500,000
9.670
760,000
14.697
Charging the System
Units are leak tested at the factory and shipped with a nitrogen
holding charge. If the holding charge has been lost due to
shipping damage, charge the system with enough refrigerant to
raise the unit pressure to 30 psig after first repairing the leaks
and evacuating the system.
After all refrigerant piping is complete and the system is
1
evacuated, it can be charged as described in the
paragraphs following. Connect the refrigerant drum to
the gauge port on the liquid shutoff valve and purge the
charging line between the refrigerant cylinder and the
valve. Then open the valve to the mid position.
If the system is under a vacuum, stand the refrigerant
2
drum with the connection up, open the drum, and break
the vacuum with refrigerant gas.
With a system gas pressure higher than the equivalent of
3
a freezing temperature, invert the charging cylinder and
elevate the drum above the condenser. With the drum in
this position and the valves open, liquid refrigerant flows
into the condenser. Approximately 75% of the total
30
Vacuum below 1 atmosphere
Mercury (mm)
Mercury (in)
760.00
29.921
759.95
29,920
759.90
29.920
759.85
29.920
759.80
29.910
759.70
29.910
759.50
29.900
759.00
29.880
758.00
29.840
756.00
29.760
754.00
29.690
752.00
29.600
750.00
29.530
745.00
29.330
740.00
29.130
730.00
28.740
710.00
27.950
660.00
25.980
560.00
22.050
260.00
10.240
0
0
Approximate fraction
of 1 atmosphere
—
1/15,200
1/7,600
1/5,100
1/3,800
1/2,500
1/1,520
1/760
1/380
1/189
1/127
1/95
1/76
1/50
1/38
1/25
1/15
2/15
1/4
2/3
1 atmosphere
requirement estimated for the unit can be charged in this
manner.
After 75% of the required charge enters the condenser,
4
reconnect the refrigerant drum and charging line to the
suction side of the system. Again, purge the connecting
line, stand the drum with the connection side up, and
place the service valve in the open position.
Important: At this point, interrupt the charging procedure and
do prestart checks before attempting to complete the
refrigerant charge.
Note: Stamp the total operating charge per circuit on the unit
nameplate for future reference.
Adding refrigerant to the suction always risks liquid-related
damage to the compressor.
Take special care to add refrigerant slowly enough to the
suction to prevent damage. Adjust the charging tank hand
valve so liquid leaves the tank but vapor enters the compressor.
H
O boiling point at each
2
o
pressure (
F)
—
–50
–40
–33
–28
–21
–12
1
15
29
39
46
52
63
72
84
101
125
152
192
212
CAUTION
McQuay IM 987
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