What do bubbles in the sight glass typically indicate?

Bubbles in the sight glass of a refrigeration or air conditioning system are generally indicative of an issue related to refrigerant flow and charge level. When there are bubbles visible, it often suggests that the system is not operating efficiently and that there may be an inadequate amount of refrigerant returning to the evaporator, which could lead to improper cooling and performance.

In the context of the answer provided, an excessive superheat setting in the TXV (Thermal Expansion Valve) can restrict the flow of refrigerant, causing the evaporator to partially fill with vapor rather than liquid. This condition can create bubbles in the sight glass, as there is insufficient liquid refrigerant to fully occupy the system’s path. A properly functioning TXV should maintain an appropriate balance to prevent bubbles, ensuring the refrigerant flows correctly and remains in the liquid state until it reaches the evaporator.

This understanding is crucial for diagnosing issues in HVAC systems, allowing for effective maintenance or adjustments to restore optimal function. The presence of bubbles can also prompt further investigation into the system's refrigerant levels and settings to ensure everything is operating as intended.