Air conditioning systems are designed to never leak refrigerant; therefore, you should never have to charge it. Of course, there are times with an air conditioning system loses refrigerant due to leaks or maintenance. Charging a 410A condensing unit is the same as charging any unit, only the refrigerant is different. It's important to remember that releasing refrigerant into the air is illegal and working with refrigerant requires EPA certification.
Connect the red hose of the manifold gauge to the high side valve on the back of the condenser. The high side is the smaller valve. Connect the blue hose of the manifold gauge to the low side access valve (the large valve on the condenser).
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Connect the yellow hose on the manifold gauge to the 410A refrigerant tank. Turn the handle on top of the tank to release refrigerant from the tank. Flip the tank upside down so that it will charge the system in a liquid state.
Make sure the air conditioner is on.
Turn the blue handle on the manifold gauge to allow the 410A refrigerant into the system. Charge to manufacturer's specifications.
Turn the blue handle on the manifold gauge to the "Off" position. Turn off the refrigerant tank. Disconnect the hoses.