[serialk11r]

If you really want efficient A/C and have good fabrication skills, you can try fitting a modern variable displacement compressor. Another strategy is to modify the existing system to reduce its output so it's more efficient when you're driving faster.

If I understand how they work correctly, slightly decreasing the amount of refrigerant in the system would make the compressor (which has a fixed pressure ratio) consume slightly less power at any given speed. It may need to be running at a higher speed before the condenser side has enough pressure to work well.

Another method is an underdrive pulley.

AFAIK, electric A/C is probably best left for retrofitting cars without A/C, since its main advantage is simplification of packaging, not efficiency or cooling effectiveness. You're going to need a pretty crazy amount of battery to run A/C for more than a few minutes.

What sort of driving are you doing where the AC is killing your mpg? At idle, I find A/C uses a pretty modest amount of fuel (like 0.1gph ish). If it's travelling at high speed with the engine turning faster, I would first look to underdriving the compressor somehow.