A Californian company that usually makes green-energy fuel cells is due to deliver 170 repaired ventilators to Los Angeles later on Monday after transforming its manufacturing process.
An engineer at Bloom Energy downloaded the service manual and taught himself how to dismantle and rebuild them in a day, the Los Angeles Times reported.
They had been in storage since the H5N1 bird flu outbreak of the mid-2000s.
Bloom says it is now working to find other stockpiles of disused machines.
On Saturday, as California Governor Gavin Newsom visited the manufacturing plant, he said: “We got a car and a truck and had [them] brought here to this facility at 08:00 this morning.
“And Monday, they’ll have those ventilators back into Los Angeles all fixed. That’s the spirit of California.”
Mr Newsom said the the original manufacturers had initially told him it would take a month to fix 200 ventilators, which help patients breathe if they are having difficulties due to Covid-19 or other diseases.
He said he told Bloom: “We challenge you to do more and do better."
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And on 22 March, the company’s chief executive, KR Sridhar, sent the governor a photo of 24 finished ventilators ready to be certified for use.
Mr Sridhar told CNBC: “We think we can do hundreds of ventilators - close to 1,000 ventilators - a week of refurbishment.
"This is the fastest way - we can take existing ventilators that are out there, get them working, get them back to the hospitals.”
The strategy contrasts with that of the UK, which is seeking to make thousands of new machines in partnership with manufacturing companies.
The UK has about 8,000 ventilators available and has placed orders for the same number again from existing manufacturers
Dyson has also received an order for 10,000 units of a new design - if it passes regulatory hurdles.
But manufacturers have said they will not be able to meet demand if coronavirus infections peak in the coming weeks.