Where should a leak detector probe be placed to check for gas leaks in a water box?

To effectively check for gas leaks in a water box, placing the leak detector probe through the drain valve is optimal. This location allows direct access to areas where refrigerant may escape, especially in systems where traditional testing on the surface may not provide the needed sensitivity to detect smaller leaks.

Using the drain valve as an entry point enables the probe to sense gas that may escape through the system's drainage points. The water box can create conditions where leaks could pool and make detection more challenging; thus, probing through the drain allows for immediate identification of any leaks potentially present.

Other choices, while they might seem suitable, would not provide the same level of access or sensitivity for detecting leaks. For example, checking at the evaporator outlet could overlook leaks that are localized below the water box, and probing through the water inlet might not reach the areas where refrigerant could pool or escape. Placing the probe directly on the water box surface might not capture escaping gas effectively, especially if the leak is coming from a substrate inside the box rather than the outer surface. Therefore, using the drain valve is the most effective method in this context.