What is the episode of friends when a heat wave hit Manhattan and Monica's generator broke?

The episode you’re referring to is "The One with the Heat Wave," which is Season 4, Episode 2 of Friends. In this episode, a heat wave hits Manhattan, causing the friends to struggle with the sweltering temperatures. Monica's apartment's air conditioning breaks down, leading to a series of humorous and chaotic events as they try to cope with the heat. Additionally, the episode features Joey and Chandler's attempts to impress a woman by turning on their own air conditioning.