If a liquid line filter drier is clogged, what will appear in the sight glass?

When a liquid line filter drier becomes clogged, the sight glass will typically show bubbles. This occurs because the clogging restricts the flow of refrigerant. As the refrigerant tries to move past the obstruction, the pressure drops, leading to the formation of vapor bubbles in the liquid line. This is an indication of inadequate flow and can signal that the filter drier needs to be replaced or serviced.

In contrast, if there were no flow, the sight glass would appear empty or show no movement, which usually indicates a complete blockage or loss of refrigerant. A clear liquid would indicate good flow and filtration, while continuous flow would show proper operation of the system. Therefore, bubbles in the sight glass are a clear sign of a problem caused by a clogged filter drier.