?'s about getting A/C Working on 75 Duster

You'll need to buddy up to a tech or get access to gauges and a vacuum pump. Pull a vacuum on the system to make shure there are no leaks (pull it down valve it off and see if it looses vacuum). If that checks out buy a 134a conversion kit (134a,oil,filler adapter) and gas it upwith the oil (shake the small can to get oil and refrigerant in). After you get some in, start the car and turn the AC on full. If the pressure switch is made the pump will pull in the mixture on its own. The conversion kits gauge has color zones on the dial to tell you when the pressure is right. Fill it up to the green zone and let it run for a while. Put the gauge back on and check it. Good to go. Check with your conversion gage periodically to make sure it good. 12 and 134a use different oils but since you had it apart it should be gone. Seals could be an issue down the road, and you will loose some capacity on the unit. Sorry thats as short as i can make it hope that helps.