Where do you add freon in a Chevrolet Malibu?

Did this to my 98 Malibu v6, the low pressure valve is on line beside fire wall behind engine, it has blue protective cap on it. high pressure valve you would not use has red cap on it located beside radiator/condenser. You don't say what year your Malibu is so this may not apply to you if your unit uses the R12 refrigerant.