What can bubbles in the sight glass indicate about the TXV setting?

Bubbles in the sight glass of a refrigeration system typically indicate a problem with the refrigerant flow. When there are bubbles present, this often signifies that the system is experiencing issues related to the refrigerant charge or the expansion device's operation, particularly with the thermostatic expansion valve (TXV).

An excessive superheat setting means that the TXV is allowing the evaporator coil to become overly hot before the refrigerant is allowed to flow through it. If the superheat level is too high, the TXV will not allow enough refrigerant into the evaporator, which can lead to insufficient cooling and bubbles forming in the sight glass. This is because there isn't enough liquid refrigerant reaching the evaporator, thus causing an imbalance that results in the presence of vapor rather than a full liquid line.

In contrast, low refrigerant charge would typically manifest as a low level in the sight glass rather than bubbles. Faulty compressor operation could present various symptoms but not specifically bubbles in the sight glass. Normal operating conditions would not cause bubbles to appear; instead, you would expect a clear sight glass indicating a proper charge of liquid refrigerant.