TM 5-2420-230-24-1
Table 19-1. Boiling Point of Water Under Vacuum
Vacuum Required To Boil Water In A/C System
Ambient Temperature F (C)
inHg (kPa)
100 F (38 C)
28 inHg (95 kPa)
90 F (32 C)
28.5 inHg (96.5 kPa)
81 F (27 C)
28.8 inHg (97.5 kPa)
70 F (21 C)
29.2 inHg (98.8 kPa)
(1)
Ensure that valves (2) and (3) are closed.
(2)
Disconnect the charging hose (6) from
inlet (7) on refrigerant service unit.
(3)
Check the oil level in the vacuum pump. Add
oil as necessary. Refer to the vacuum pump
OEM manual for the correct procedure.
(4)
Connect charging hose (6) to inlet (9) on
vacuum pump.
(5)
Open valves (2) and (3) completely. Turn
valves (2) and (3) counterclockwise to open.
(6)
Evacuate A/C system. Refer to vacuum
pump OEM manual for operation
instructions.
NOTE
At high elevations, less vacuum is required.
28 inHg to 29 inHg (95 kPa to 98 kPa) is the
required specification at sea level. For every
1,000 ft (305 m) above sea level, decrease
the required specification by 1 inHg (3 kPa).
(7)
Operate the vacuum pump until the low
pressure gauge (10) indicates a vacuum
between 28 inHg to 29 inHg (95 kPa to
98 kPa).
(8)
After the vacuum in the A/C system reaches between 28 inHg to 29 inHg (95 kPa to 98 kPa), operate vacuum
pump for a minimum of 90 min.
NOTE
The evacuating procedure removes air and moisture from the system. Do not use the vacuum pump
primarily to indicate a system leak.
(9)
If the specific vacuum cannot be reached, the A/C system may have a leak. Repair all leaks and repeat Steps (1)
through (8).
19-6