If a capillary tube breaks between its sensing bulb and the expansion valve, what happens to the expansion valve?

When a capillary tube breaks between the sensing bulb and the expansion valve, it leads to a loss of refrigerant pressure in that section of the system. The sensing bulb is designed to detect the temperature of the refrigerant, and it relies on the pressure within the capillary tube to function correctly.

In the event of a break, there is an immediate drop in pressure at the sensing bulb, because it can no longer receive the refrigerant necessary to maintain proper sensing capabilities. This drop in pressure causes the expansion valve to close completely. As a result, the refrigerant flow to the evaporator is severely restricted, which can lead to a number of issues, including possible freeze-up if not addressed.

The complete closure of the expansion valve is a protective measure, as the system is unable to accurately sense or control the refrigerant flow due to the failure in the capillary tube. This response helps prevent further problems within the system until the issue can be resolved.