I really can't speak for all hostels in Spain, but most of them do not have air conditioning I don't think. Few have self-operation either. I do recall that Hostal Persal
(pricey, but more like a hotel) next to the Plaza Santa Ana has individual A/C units in each window.
Those which do often only run it in the early evening hours and then it's shut off for the night. Remember, while summer months in Madrid can be HOT, the air is dry and less uncomfortable, especially at night.
Good luck and please let us know what you found during your stay. Thanks!
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