Should car air conditioning refrigerant be added from the low-pressure or high-pressure side?

[Shannon]

Refrigerant can be added to a car's air conditioning system from either the low-pressure or high-pressure side. Important notes: When adding refrigerant from the low-pressure side, the refrigerant must be in gaseous state. When adding from the high-pressure side, the compressor must not be running, and the refrigerant must be in liquid state. Additional information follows: Freon is a common refrigerant: When a car's air conditioning isn't cooling properly, adding refrigerant can restore cooling performance. Determining when to add refrigerant by observing the sight glass on the receiver-drier: During normal AC operation, bubbles in the sight glass indicate insufficient refrigerant and the need for recharge. If excessive bubbles appear, besides adding refrigerant, a leak check should also be performed.