The Smart-ChargeTM A/C Recharge Kit electronically tells you the status of your cooling system in seconds. Screw in a canister of R-134a to the handheld gauge and use the trigger to dispense refrigerant into system. Releasing trigger automatically tests the system. Keep charging till you get the green light and you're ready to go. Convenient Push LockTM connector makes connecting to even the most hard-to-reach A/C service ports a snap. Accurately measure and charge your A/C system. Just press the trigger and let Smart Charge do all the work.