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 TM 55-1905-219-14-8
4-28. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
(e) Continue dehydrating until a temperature of 35F (1.7 ) is reached on vacuum indicator
C
(corresponding to a vacuum of .2" Hg (0.675 kPa ) absolute pressure). The time required to complete
dehydration depends on the amount of moisture in the system and the size of the plant. The operation will
probably take from 18 to 72 hours. If a temperature of 35F (1.7 ) cannot be reached on the vacuum
C
indicator, it may be due to one or more of the following faults:
1 Leak in system or connecting tubing to vacuum pump.
2 Closed line valves.
3 Inefficient vacuum pump.
4 Defective vacuum indicator.
(f) With pump still running, open system at a point furthest from pump and admit air through a dryer.
Close system and repeat steps (d) and (e). Moisture left in the system can thus be greatly diluted and almost
completely removed by "double dehydration".
(g) When dehydration is completed, close shut-off valve at vacuum indicator, charging valve, shut-off
valve at vacuum pump and stop pump in that sequence. Do not allow pump to operate longer than absolutely
necessary after connection is broken. Disconnect vacuum pump and vacuum indicator.
4-869
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