Transitioning to a sustainable and equitable electricity sector requires an understanding of the impacts on energy equity and vulnerable populations under a warming climate. Air conditioning (AC) is a vital climate adaptation measure for vulnerable populations, but AC usage results in higher household energy costs. We use May 2017-April 2018 smart-meter data from Phoenix, Arizona, to derive household-level temperature response functions across income, race/ethnicity, and age. We then simulate how electricity usage may change under two climate change scenarios from 2020-2070 (Representative Concentration Pathways (RCP) 4.5 and 8.5). We estimate both the short-run effects (change in usage from only temperature) and long-run effects (AC efficiency upgrades to aid in coping with a warming climate). In the short-run and under RCP 8.5, the median household experiences a percentage change increase of 27.7% (16.7% to 38.0%) in annual summertime electricity consumption relative to their 2017-2018 baseline. Yet, the median elderly and low-income household percentage changes are nearly 5 percentage points higher than their counterparts after controlling for decadal, housing, and cooling infrastructure. In the long run, improving AC efficiency reduces the short-run cooling consumption by 70% for vulnerable groups. Yet, even with AC efficiency improvements, low-income groups’ energy burden is reduced by only 1-2 percentage points. This indicates that AC efficiency and cost structure changes are needed to allow households to adapt to a warming climate.