I just inherited a carrier model# 30gtn100 This unit has two sight glasses. One is located right after a two core liquid line drier and the second is located in part of the EXVs body. The first sight glass does not flash at all and always has a full column of liquid no matter how many compressors and fans are running. The other sight glass that is located in the exvs body constantly flashes and never runs a full sight glass. Im just curious of the purpose of the second sight glass. The sight glasses are less than three feet apart.