President Garfield: From Radical to Unifier by C. W. Goodyear:
Not all callers were turned away. A few citizens approached the White House staff in early July with ideas on how Garfield’s room might be artificially cooled—no small feat in a Washington summer. A machine shop staffed by naval engineers started droning away in the cellar to cobble their designs together. After some trial and error—necessary steps in invention—they produced a fan-powered apparatus that forced ambient air through fabric saturated with ice and salt. Garfield’s doctors switched it on to find the device cooled their space by almost thirty degrees. It was the first air-conditioner.