Refrigerant Multi-Key for Use with All Novent NG / NP / NPE Euro and NS Universal Locking Caps. Tamper Resistant / Locking Caps (sold separately) offer a unique way to prevent access by unauthorized individuals and or miss use. Service tech, Installer or DIY er must have. The HVAC Multi Key Tool is a versatile tool designed for the installation and removal of locking caps used in HVAC systems that use 410A and R22 refrigerants. This 2-in-1 tool provides convenience and efficiency by eliminating the need for multiple tools.It simplifies the process and saves you time and effort