My Wife's 74 1.8 had a DPD AC system on it when she got it. It always was marginal with the stock compressor and R12. When I restored it, I put in all new hoses, new O-rings, a new dryer, and a rotary compressor running R134a. Now on a 100 degree Texas summer day, it will turn you into a popsicle. If you are going to do this I suggest the rotary compressor conversion kit for a type IV available from ICEAC.
www.iceac.com It really fits and works great.