Which valve arrangement is least likely to cause refrigerant loss from the refrigeration system?

A valve arrangement that is on the back seat position is designed to allow for minimal refrigerant leakage when the valve is closed. This position keeps the valve's sealing surface engaged within the valve body, creating a tight seal that significantly reduces the chance of refrigerant escaping from the system.

In contrast, a fully open service valve does not provide any restriction to refrigerant flow and could lead to loss during maintenance or if any disconnection occurs. A partially open service valve might allow for some refrigerant escape, especially if pressure builds up or if there's a need to release pressure. The liquid line shutoff valve, while important for controlling liquid refrigerant flow, could also be subject to leakage if not properly sealed.

The emphasis on the back seat position is crucial, as it is a design feature specifically intended to protect the integrity of the refrigeration system by minimizing refrigerant loss, making it the least likely configuration to result in refrigerant escaping.