TM 9-4120-371-14
2-3. INDICATORS
The refrigerant sight glass (fig. 22) 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.
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.
