If there were any changes to the ac in kingdom halls we would see it in an elders letter. My friend says that he has been to a few halls recently visiting friends and all the halls are nicely air conditioned. He says the elders control the temperature and often its based on their personal preference. Over the years he has seen some halls with people cooling themselves with the watchtower magazine and some halls the sisters bringing blankets and sweaters etc. He said he had one elder that didn't like it cold and so he had trouble not sweating at the meeting because the temp was set to high.