It seems Tesla didn't speak or write anymore publicly about his ambient heat engine after the article in 1900, but apparently kept working on it until around 1930 ?
I don't know any more than what he put in that article.
What seems interesting to me about compressed air is as the air is compressed there is the heat of compression that could be recovered and used towards running a Stirling engine.
Then there is the compressed air that can be used to drive air equipment, or whatever, partly re-expanded by ambient heat.
But the combination of re-expansion of the air with work output produces cold, that could also be used to run a Stirling engine.
And there is the output from the Stirling engine running on the temperature extremes produced by compressing and re-expanding the air.
Under most circumstances a heat pump is used for heating or cooling and the other product is thrown away.
But an air cycle system heat pump combined with a Stirling engine seems like a low hanging fruit that takes just a low tech compressor and a low tech Stirling engine, basically achieving Tesla's "Self-acting" ambient heat engine without the necessity for precision turbines that can operate at 250,000 RPM surpassing the speed of sound and other potential difficulties.
I think this guy may have just accomplished it with just an old Briggs and Stratton engine, a refrigeration expansion valve a compressor and some check valves and pipe.
https://youtu.be/CJcGqHqs4-Q