Battery indicator on and no A/C

[TheLotus]

'94 RT-10.
Battery indicator in message center came on and A/C will not work. Turn off A/C and indicator goes out. Battery is Ok and new. Alternator output appears OK. Voltmeter indicates OK. I am stumped

 

[Viper Wizard]

Vipering,
It may be an internal Diode that has opened in the Alternator? I've had that one before! It's time for a new Alternator.