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Dec. 1, 2009
Moisture Indicators and Sight Glasses

Q: I have a new HMI sight glass that is showing a wet condition, right out of the box. Can I use this in my system and will it give the proper moisture ndication?

A: The element in the sight glass senses the moisture of the atmosphere that it's in. In this case, the air has enough moisture to turn the sensing element pink (wet).

Once a sight glass is put into an operating refrigeration system, it will adjust its color over time to indicate the moisture level of the refrigerant. This change can take several hours to occur; it will not happen instantaneously.

Q: If I pull a vacuum on the system with the wet sight glass, will that change its color back to dry?

A: Pulling a vacuum by itself will not remove enough moisture from the HMI indicator to effect a color change in a short period of time. The recommended procedure is to install the HMI in the system with a new EK filter drier and clean, dry refrigerant, and operate the system. Within several hours the indicator will show the moisture condition of the refrigerant. It's recommended, however, to allow the system to operate for 12 hours to attain complete equilibrium.

©2005 Emerson Climate Technologies, Inc. Used by permission.