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2-3.
TM 5-4120-377-14
Figure 2-2. Operator's Controls Rear
The refrigerant sight glass (fig.2-2) is the only visual indicator used on the Model F18T4-2S and Model F18T4-2S and Model 3788
Air Conditioner. The sight glass is a port or window through which the refrigerant condition can be seen.
Liquid refrigerant actually flows through the sight glass chamber only during cooling cycles when the air
conditioner is in operation in the COOL mode. The unit must be operated approximately 15 minutes in maxi-
mum cooling prior to checking condition of refrigerant at sight glass. The sight glass is equipped with a center
indicator that is moisture sensitive. Dry refrigerant is indicated by green, it turns to chartreuse when the
moisture content becomes undesirable, and to yellow when the level becomes unacceptable. Excessive
moisture in the refrigerant may damage or possibly destroy the compressor. If the liquid refrigerant observed
in the sight glass has an opaque, milky appearance, or frequent bubbles appear, the volume of refrigerant
is low and the system should be charged. Either moisture or low charge indications should be reported to
direct support maintenance.
Do not operate the air conditioner in the COOL mode if the refrigerant color has reached
the yellow band or if numerous bubbles appear in the sight glass. COOL mode operation
may be continued with the refrigerant color in the chartreuse band or with only an
occasional bubble appearing in the window, but the sight glass should be rechecked after
each four hours of operation to insure that the condition has not become worse.
2-3
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