Which condition is least likely to occur in a system with a restricted capillary tube?

In a system with a restricted capillary tube, the condition that is least likely to occur is flood back to the compressor. A capillary tube is designed to control the flow of refrigerant into the evaporator, and significant restrictions within this tubing can lead to a host of pressure-related issues.

When the flow of refrigerant is restricted, the suction pressure tends to drop because less refrigerant is available to evaporate in the evaporator, which results in reduced heat absorption. As the pressure in the evaporator lowers, the discharge pressure may actually increase due to a higher pressure buildup on the condenser side; this is often due to the compressor working harder to pull in refrigerant with insufficient flow to the evaporator.

Furthermore, with reduced flow into the evaporator, there is a higher chance of not all the refrigerant evaporating before it reaches the compressor, which could theoretically lead to some liquid reaching the compressor. However, since the overall flow is restricted, the likelihood of excessive liquid refrigerant flooding back to the compressor is minimized because the system is not allowing enough refrigerant to cycle properly. Thus, flood back is not expected to happen as a common consequence of a restricted capillary tube system.