30
McQuay IM 987
Mechanical Installation
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.
1
After all refrigerant piping is complete and the system is
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.
2
If the system is under a vacuum, stand the refrigerant
drum with the connection up, open the drum, and break
the vacuum with refrigerant gas.
3
With a system gas pressure higher than the equivalent of
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
requirement estimated for the unit can be charged in this
manner.
4
After 75% of the required charge enters the condenser,
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.
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.
Table 7: Pressure-Vacuum Equivalents
Absolute pressure above zero
Vacuum below 1 atmosphere
Approximate fraction
of 1 atmosphere
H
2
O boiling point at each
pressure (
o
F)
Microns
PSIA
Mercury (mm)
Mercury (in)
0
0
760.00
29.921
—
—
50
0.001
759.95
29,920 1/15,200
–50
100
0.002
759.90
29.920
1/7,600
–40
150
0.003
759.85
29.920
1/5,100
–33
200
0.004
759.80
29.910
1/3,800
–28
300
0.006
759.70
29.910
1/2,500
–21
500
0.009
759.50
29.900
1/1,520
–12
1,000
0.019
759.00
29.880
1/760
1
2000
0.039
758.00
29.840
1/380
15
4,000
0.078
756.00
29.760
1/189
29
6000
0.117
754.00
29.690
1/127
39
8,000
0.156
752.00
29.600
1/95
46
10,000
0.193
750.00
29.530
1/76
52
15,000
0.290
745.00
29.330
1/50
63
20,000
0.387
740.00
29.130
1/38
72
30,000
0.580
730.00
28.740
1/25
84
50,000
0.967
710.00
27.950
1/15
101
100,000
1.930
660.00
25.980
2/15
125
200,000
3.870
560.00
22.050
1/4
152
500,000
9.670
260.00
10.240
2/3
192
760,000
14.697
0
0
1 atmosphere
212
CAUTION
Adding refrigerant to the suction always risks liquid-related
damage to the compressor.