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 TM 55-1905-220-14-8
4-29. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
liquid refrigerant flow through sight glass. If bubbles appear, additional refrigerant is-
required. If a solid column of liquid appears, the refrigerant charge is sufficient.
9 To completely empty a refrigerant drum, pressure in drum must be greater than pressure in
liquid line. As drum is emptied, pressures equalize. To maintain a pressure difference great
enough to force refrigerant into liquid line, heat drum with steam or hot water. 10 When a
drum has been emptied and it is necessary to connect another drum to complete charging,
close charging valve and drum valve. Stop compressor and disconnect empty drum.
Connect a new drum as per step (5) and resume charging.
11 When required amount of refrigerant has been charged, close drum valve. Allow compressor
to stop by action of low pressure cut-out switch. Close charging valve. Close dryer outlet
valve and open dryer bypass valve. If dryer has no bypass, open dryer inlet valve. Place
suction pressure regulator(s) in operation by opening cut-out valves and closing bypass
valve. Allow compressor to operate until normal operating conditions are reached. Then,
check liquid level in receiver. There should be enough liquid refrigerant in bottom of receiver
to prevent passage of refrigerant gas into liquid lines. If there is no liquid in receiver,
reposition valves and charge additional refrigerant.
12 When sufficient refrigerant has been charged, close charging valve. Close drum valve and
disconnect charging line and drum. Close dryer outlet valve and open dryer bypass valve. If
dryer has no bypass, open dryer inlet valve. Store empty refrigerant drums for re-use.
(5) Removing Refrigerant.
(a) Refrigerant-12 may be removed from the system through the refrigerant drain valve. The charging
valve is often installed at a low point in the system so that it can also be used as a drain valve or a separate
drain valve in the main liquid line is provided.
(b) With all refrigerant system valves in their normal operating positions, proceed as follows to drain
refrigerant:
1 Shut off liquid supply to evaporator(s). Close dryer bypass valve, open dryer inlet valve, and
be sure dryer outlet valve is closed. If dryer has no bypass, close heat interchanger liquid
inlet valve and be sure that heat
4-872
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