where is the valve to attaché hose and gage to refill refrigerant?

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I have a container of EZChill Auto Air Conditioning R-124a Refrigerant to go into my Mazda 626 but do not remember where the valve is on the car to attach the hose with gage. Where can I find a schematic or directions of correct placement. I did this last year but can't figure it out now? I have a slow refrigerant leak.