JOHNSON CONTROLS
18
Form 160.78-O1
Issue date: 05/19/2021
Section 3 - Maintenance
Vacuum testing
Ensure power is removed from the input
side of the VSD at all times when the
chiller is under vacuum (less than atmo-
spheric pressure). The VSD maintains
voltage to ground on the motor when the
chiller is o while voltage is available to
the VSD. Insulating properties in the mo-
tor are reduced in vacuum and may not
insulate this voltage suciently.
After the pressure test has been completed, the vacuum
test should be conducted as follows:
1. Connect a high capacity vacuum pump, with in-
dicator, to the system charging valve as shown in
Figure 5 and start the pump. See Vacuum dehy-
dration in this section.
2. Open wide all system valves. Be sure all valves to
the atmosphere are closed.
3. Operate the vacuum pump in accordance with
Vacuum dehydration in this section until a wet
bulb temperature of 32°F (0°C) or a pressure of 5
mm Hg is reached. See Table 1 for corresponding
pressure values.
4. To improve evacuation circulate hot water, not
to exceed 125°F (51.7ºC) through the evapora-
tor and condenser tubes to thoroughly dehydrate
Table 1 - System pressures
*Gauge Absolute
Boiling
temperatures
of
water
°F
Inches of
mercury (Hg)
below one
standard
atmosphere
psia
Millimeters
of mercury
(Hg)
Microns
0 in. 14.6960 760.00 760,000 212
10.240 in. 9.6290 500.00 500,000 192
22.050 in. 3.8650 200.00 200,000 151
25.980 in. 1.9350 100.00 100,000 124
27.950 in. 0.9680 50.00 50,000 101
28.940 in. 0.4810 25.00 25,000 78
29.530 in. 0.1920 10.00 10,000 52
29.670 in. 0.1220 6.30 6,300 40
29.720 in. 0.0990 5.00 5,000 35
29.842 in. 0.0390 2.00 2,000 15
29.882 in. 0.0190 1.00 1,000 1
29.901 in. 0.0100 0.50 500 -11
29.917 in. 0.0020 0.10 100 -38
29.919 in. 0.0010 0.05 50 -50
29.9206 in. 0.0002 0.01 10 -70
29.921 in. 0 0 0
*One standard atmosphere = 14.696 psia
= 760 mm Hg absolute pressure at 32°F
= 29.921 in. Hg absolute at 32°F
Notes: psia = lb per sq. in. gauge pressure
= Pressure above atmosphere
psia = lb per sq. in. absolute pressure
= Sum of gauge plus atmospheric
pressure
Water
Freezes
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