ESCO Air Conditioning Practice Exam

When a TEV or capillary tube is used as a metering device, a low refrigerant charge will cause:

1. Equal head pressure

2. High head pressure

3. Low head pressure

4. Variable head pressure

The correct answer is: Equal head pressure

When a TEV (Thermostatic Expansion Valve) or capillary tube is used as a metering device, a low refrigerant charge will cause equal head pressure. This is because a low refrigerant charge in the system results in less refrigerant flowing through the system, leading to reduced heat absorption and a lower evaporating pressure. This lower evaporating pressure is sensed by the evaporator pressure regulator in the TEV, causing the valve to open more to allow more refrigerant into the evaporator to balance the system. As a result, the head pressure remains equalized to maintain the system's overall balance and efficiency. Options B, C, and D are incorrect because they do not reflect the typical response of the system to a low refrigerant charge when a TEV or capillary tube is used as the metering device. High head pressure, low head pressure, or variable head pressure are not the expected outcomes when there is a low refrigerant charge in this setup.