What is the effect on the TEV if the bulb loses its charge?

When the sensing bulb of a thermal expansion valve (TEV) loses its charge, it can no longer accurately sense the temperature of the refrigerant vapor. The bulb's function is critical for modulating the movement of the valve's pin which controls the flow of refrigerant into the evaporator based on the temperature it detects.

Without the charge in the bulb, the pressure inside it will drop, causing the valve to react as if it is sensing low load conditions. This situation results in the TEV closing, thereby restricting the flow of refrigerant into the evaporator. A decreased flow of refrigerant can lead to inadequate cooling performance and may cause the evaporator to temperature drop lower than required, potentially leading to other operational issues.

This understanding highlights how crucial the charged bulb is to the proper functioning of the TEV and refrigerant flow management in HVAC systems.