| Tweet |
Custom Search
|
|
|
||
 TM 55-1905-220-14-8
4-29. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).-
(c) Before dehydrating a system, make the following preparations and keep in mind the following
points:
1 The best means of dehydration is by evacuation with a pump especially built for the purpose.
Obtain a pump that will produce a vacuum of .2" Hg absolute. Do not use the compressor as
a vacuum pump. It is not designed for such use and may be seriously damaged.
2 Pressure test the system to be sure it is free of leaks. Refer to paragraph o. When installing
the vacuum pump, make sure that there is no leak in the tubing connecting the pump to the
system.
3 Obtain a vacuum indicator. The vacuum indicator is described below.
4 Keep ambient temperature above 60 (15.6 ) to speed the evaporation of moisture.
F
C
CAUTION
Do not attempt dehydration if ambient temperature is below
60 (15.60 ). Moisture may freeze in the system.
F
C
5 Carefully follow the dehydration procedure, paragraph (3). Be sure to open all stop valves so
that no part of the system will be blocked off.
6 Frequently, valuable time is spent in dehydrating a system in which refrigerant is held in
solution with the oil in the compressor crankcase. This usually does not apply to a newly
installed system, since only a small holding charge of refrigerant is present in the crankcase.
When it is necessary to dehydrate an existing system after repairs, drain the oil from the
compressor crankcase. Replace with new oil after dehydration.
(2) Vacuum Indicator.
(a) The vacuum indicator consists of a wet-bulb thermometer in an insulated glass tube
containing distilled water. Part of the tube is exposed so the thermometer can be read and the water level
checked. When the vacuum indicator is connected to the vacuum pump suction line, the thermometer reads
the temperature of the water in the tube. The temperature is related to the absolute pressure in the tube. The
table below gives the absolute pressures corresponding to various
temperature.
4-896
|
||
|
||
