SUPCO Model # SSGSS2* Supco SSGSS2 Universal Liquid Moisture Indicator Site Glass 1/4" GemTech SLM1TT2* For optimum performance a cooling system must have a solid column of light at the expansion valve. * A sight glass provides a visual indicator of any "bubbles" in the refrigerant stream that could adversely effect performance. * In general, the sight glass should be located as close to the expansion valve as possible. * Sight glasses also incorporate a visual moisture indicator which changes color if moisture is rises to an unacceptably high level.