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 TM 55-1905-219-14-8
4-28. 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
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