What position should a three-way service valve be in during evacuation?

During evacuation, the appropriate position for a three-way service valve is the mid-position. In this configuration, the valve allows for the refrigerant to flow out of the system into the vacuum pump while simultaneously enabling air and moisture to escape from the refrigeration system. This optimal setup ensures that all contaminants are effectively removed, facilitating a successful evacuation process.

In contrast, if the valve were closed, the evacuation process would be impeded, as the vacuum pump would not have access to the entire system. Alternatively, having the valve fully opened might not yield the desired results either, as it could potentially create a situation where the flow is unrestricted, making it difficult to adequately achieve the required vacuum level. The mid-position is thus essential to effectively balance flow, ensuring both proper evacuation and protection of the system’s integrity.