1988 Honda Accord Air Conditioner, why won't the line take any refrigerant?

I bought the right hose along with the conversion kit to put it on an old R-12 system. My brother-in-law is a plane mechanic and does alot of work on his cars as well and when he went to load the first can of lubricant/refrigerant the line didn't want to take it. We connected it to the correct line, what could be wrong here?