The product is designed for AUTO AC refrigerant recharging. This reliable and durable component is a must-have in your automobile DIY toolbox.<br>User Instructions:Prior to placing R134a can tap onto R134a can, screw handle counter clockwise until the piercing stem is above the seal. Thread the R134a can tap onto the R134a can. Attach a R134a changing hose. Always add refrigerant to low side of A/C system. Turn the handle on the R134a can tap clockwise until the piercing stem pierces the R134a can. To start refrigerant flow, turn handle on R134a can tap counter clockwise until the valve opens. Turn R134a can tap handle clockwise until it stops to close R134a can tap before removing R134a hose.