York YMC2 A, Operation And Maintenance

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 off while voltage is available to 

the VSD. Insulating properties in the mo-

tor are reduced in vacuum and may not 

insulate this voltage sufficiently.

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