HVAC Excellence Commercial Air Conditioning ESCO Certification Practice Exam

In a system using a capillary tube as a metering device, the flow of refrigerant to the evaporator is directly influenced by pressure differences throughout the refrigeration system. During the off-cycle, the system stops feeding the evaporator when the high and low pressures within the system balance out.

When the high-pressure side and low-pressure side reach equilibrium, there is no longer a pressure differential to push the refrigerant through the capillary tube, effectively halting the flow to the evaporator. This is a crucial operational aspect of capillary tube systems, as they rely on such pressure differences to function correctly.

Understanding this principle is vital for troubleshooting and servicing HVAC systems, as recognizing when flow stops can aid in diagnosing issues during the off-cycle. Other factors, such as the receiver being empty or the accumulator running out, affect operation in different ways, but the balancing of high and low pressures is the defining mechanism for ceasing refrigerant flow through the metering device in this context.