It was 94 degrees on the 11th floor of the Paterson Houses when a 77-year-old man died.
His apartment in the Paterson Houses had been without air conditioning for two days.
The air conditioning has been restored, but residents are still heated.
"It was hot! I had no air. Off and on, off and on," said neighbor, Christine Johnson.
There has been no official cause of death yet.
The mayor says, the management was working on the problem, and had ordered a backup generator.
The building was evacuated on Thursday evening, but there are concerns it was not soon enough.
"Is 24 hours fast enough time to evacuate the building when you know it has been 95 degrees or higher? In my opinion, no. Absolutely not," said Paterson Mayor Jeffrey Jones.
A city investigation has determined so far that a PSE&G regulator near 40th Street in Paterson failed to maintain flow of electric current.
As a result there was not enough electricity to supply AC chillers in the building with enough power to run the system.
"The management company and the utility company seem to have had some type of responsibility in this at this point in time. We're not able to say who had what responsibility as of yet," Mayor Jones said.