'97 Es300 Air Conditioning On, Low Battery Voltage

[oles0012]

As noted in topic title, I have a '97 es300 which has just short of 170k miles. For about a week it sounded like it was getting barely enough juice to start the ignition, but never died on me when driving. A couple days ago, the starter clicked on me, implying I needed a new battery. Replaced the battery, voltage read '14' after starting the car, which looked good. turned on the radio, headlights, and air conditioning and the voltage dropped to '12'. Bought a refurb'ed alternator, put that in. Same deal: Read '14', until I turned on all the extras, and it dropped to '12'. I narrowed it down to only having a problem when I turn on the air conditioning. The odd thing is, I can rev the engine up to around 3k plus and it will bump back up to '14' volts. But in idle it stays at '12'. Battery terminals also cleaned off. Help anyone?