280Zx Air Conditioning Compressor,and Alternator, Lights On

[280z300hp]

I have a 1979 280zx and would like advice on compatible ac compressor for L28 engine and alternator. The  brake, fuel, door and charge lights on, and charges at 14 volts at >2000rpm but those lights go off and charge light goes on at idle and volts go to 11, so I assume the voltage relay in the alternator is u/s. Thanks in advance for any help.