What is the function of the protective cap in a service valve?

The protective cap in a service valve serves the essential function of sealing off the valve after servicing has been done. When a technician services an air conditioning or refrigeration system, they often need to open the service valve to either add refrigerant or to check the system pressures. Once this work is completed, replacing the cap ensures that the valve is not left exposed, which helps maintain the system's integrity. This sealing action prevents refrigerant leaks and protects the valve from environmental contaminants, such as dust and moisture, that could affect the system's performance.

While other options might touch on important functions related to the service valve—like preventing contaminants or controlling refrigerant flow—those are not the primary purpose of the cap itself. The cap is specifically designed to close off the valve, ensuring that it remains in good working condition and the system operates effectively.