TM 9-4120-357-14
1. Presence of water vapor in the system. Continued pumping will correct this problem.
2. Leaks in
refrigeration system. Break the vacuum with dry nitrogen, and retest for leaks.
3. Internal leakage of vacuum pump. Test pump by blocking off vacuum intake and continuing to pump.
If pump still fails to reach 500-Microns, pump is faulty.
(b) With the suction line service valve closed, disconnect the vacuum pump and attach a
cylinder of
dry nitrogen.
Leave the connection to the suction service valve loose, and turn on the cylinder shutoff valve for a few seconds to
purge the line of air. Tighten the connection, and crack the suction line service valve open slightly to break the vacuum.
Leave in this configuration until the system reaches atmospheric pressure (760 mm) , then close
the suction service valve and cylinder shutoff valve, and disconnect the nitrogen cylinder.
(c) Reconnect the vacuum pump to the suction line service valve gage port, and start the pump. Open the suction
line service valve, and again pump until a 500-Micron vacuum is achieved. This double evacuation will remove all
traces of water vapor from the system. Close the suction line service valve, and disconnect the vacuum pump. Close
the discharge line service valve, and remove the vacuum gage.
(d) Connect a cylinder of refrigerant, R22, loosely to the discharge line service valve, and turn the cylinder shutoff
valve on for a few seconds to purge the line of air. Tighten service valve connection. Charge refrigeration system as
directed in the following steps:
1. Place the refrigerant cylinder on a scale of sufficient capacity, with the shutoff valve down, or suspend the cylin-
der from a spring scale or beam scale, with the valve end down.
2. Weigh the cylinder, and record the weight.
3. Open the discharge line service valve, and slightly open the refrigerant cylinder shutoff valve. Liquid refrigerant
will be sucked into the refrigeration system rapidly at first, then more slowly as pressures begin to equalize. When 25
pounds (11.4 KG) of refrigerant have flowed into the refrigeration system, as indicated by the scale, close the discharge
line service valve and the cylinder shutoff valve.
WARNING
Hearing protection must be worn when maintenance is performed while air conditioner is
in operation. Failure to heed this warning can result in hearing loss or injury.
CAUTION
Connect power to unit as soon as possible after charging or any period when power has
been disconnected. Allow heater time to vaporize refrigerant in compressor before opera-
tion in COOL mode. If knocking or pounding is heard at start of COOL mode, turn selec-
tor switch to OFF or VENTILATE at once and allow additional warm up time.
(e) With power connected to the air conditioner, turn the mode selector switch to cool. Turn the temperature control
thermostat to maximum decrease position. With compressor operating, observe the sight-glass liquid indicator. If bub-
bles or milkiness appear, top off the refrigerant charge as follows:
1. Connect a cylinder of refrigerant, R22, loosely to the gage port of the suction line service valve, and open the
cylinder shutoff valve for a few seconds to purge the air from the line.
2.
With the air conditioner compressor operating, open the suction line service valve and the cylinder shutoff valve
to charge refrigerant gas into the system, while observing the sight-glass liquid indicator.
3. When liquid in sight-glass indicator runs clear and free of bubbles close the suction line service valve and the
cylinder shutoff valve.
4. Disconnect refrigerant cylinder, and replace caps on both service valves.
i. Final Assembly. Replace external panels, as applicable in the following manner:
(1) Position top panel on the air conditioner, and secure with screws and washers.
(2) Position front access panel, with its lower edge behind the step in the base plate, and push into contact with the
casing. Secure with four panel fastener screws.
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