A cap tube is ineffective on most commercial refrigeration systems because:

The capillary tube, often referred to simply as a cap tube, is a common component in refrigeration systems, particularly in smaller systems like household refrigerators or some low-capacity commercial applications. However, it has limitations in more demanding commercial refrigeration settings.

The reason the capillary tube is ineffective on most commercial refrigeration systems is that it cannot respond to the refrigerant needs under heavy loads. Capillary tubes have a fixed and relatively narrow diameter, which restricts the flow rate of the refrigerant to a specific capacity. In situations where the refrigeration load increases significantly, the capillary tube is unable to supply the additional refrigerant needed to maintain efficient operation. This inflexibility leads to inadequate cooling performance, making them unsuitable for larger, more complex commercial refrigeration applications that experience variable loads.

Thus, while the design of a capillary tube does lead to some complexity in terms of system management, it is primarily the inability to adapt to varying refrigerant demands under heavy loads that limits its use in commercial refrigeration systems.