The closing is expected to cost the casino several million dollars.
"It's certainly going to be a big impact," said Mark Juliano, CEO of Trump Entertainment Resorts. "Our revenue is usually $3.5 to $4 million on a weekend like this."
The loss of air conditioning could not have come at a worse time for the nation's second-largest gambling market - in the middle of the summer season, when casinos take in the most revenue from gamblers and overnight guests.
Juliano said the casino will reopen at 4 p.m. Sunday, and the 906-room hotel tower some time after that, depending on how quickly temporary equipment can cool the high-rise. Reservations will be accepted Sunday morning and check-ins allowed Sunday evening, he said.
Trump Plaza and Caesars Atlantic City have been without air conditioning since early Thursday morning. A Caesars spokesman said the casino had hooked up to a temporary air conditioning truck shortly after 4 p.m. Friday, and expected the building to be closer to normal on Saturday.
"There should be a noticeable difference in the building," spokesman Christopher Jonic said.
A Melissa Etheridge concert scheduled for Caesars on Saturday has been moved to the House of Blues, a nightclub inside the Showboat Casino Hotel, which is also owned by Caesars' parent company.
Juliano said there was little debate about the need to close the casino and the hotel, although two bars and a handful of restaurants were allowed to stay open.
"It was an environment we couldn't have employees or customers in," he said. "Once it got to 90, it was time to close."
Inside the casino, the slot machines and gambling tables were cordoned off with yellow caution tape like that used by police at crime scenes. The air was scorchingly hot as casino security waved away a few stragglers who sought to go inside.
Debbie Azevedo and William Ralph traveled from Boston to stay at Trump Plaza - their first trip here in 15 years - only to be turned away.
"I'm really upset," she said. "I looked forward to coming in here and winning a big jackpot. I guess we're going to the Sands now."
Uh, no. The Sands was blown up in 2007 to make way for a new casino that was never built.
A leaky pipe at a nearby power plant that provides cold water to the casinos to power their cooling systems was to blame for this weekend's problems. Tom Foley, Atlantic City's emergency management director, said the pipe was being excavated, and it will take four to six weeks to be completely fixed. Temporary cooling trucks will provide air conditioning to the casinos and Boardwalk Hall, a concert hall until then.
Pepco Energy Services, the plant's owner, said it restored cooling Friday to a shopping mall, The Pier Shops at Caesars.
Trump Plaza guests were being transferred to two other casinos the company owns in Atlantic City, the Trump Taj Mahal Casino Resort and the Trump Marina Hotel and Casino.
It is extremely rare for an Atlantic City casino to close down temporarily. Aside from the three-day state government shutdown in 2006, the only other time in recent history that casinos shut down briefly was when Hurricane Gloria moved up the East Coast in September 1985, according to Dan Heneghan, a spokesman for the state Casino Control Commission. The storm eventually veered harmlessly out to sea.
In the 1980s, Caesars was shut down for one day as a penalty for regulatory violations, Heneghan added.
The lack of air conditioning has already canceled three episodes of a nightly variety show that Trump Plaza offers. And a Friday night dance competition at Boardwalk Hall, which also was without air conditioning, was transferred to Resorts Atlantic City, a casino at the opposite end of the Boardwalk.