TM 9-4120-403-14
2-3. INDICATORS
The refrigerant sight glass (fig. 2-2) is the only visual indicator used on the 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 maximum 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.
CAUTION
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 re-checked after each four
hours of operation to ensure that the condition has not become worse.
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