Having lived in Japan for several years - whose summers are
significantly hotter and more humid than the UK's - and having traveled on numerous Hitachi rolling stock across the country, I can tell you right now that (if specced correctly) their aircon works absolutely fine on more urban routes.
As a throw-away observation, the aircon units on the 385 look
visually very similar to many of units that seem to be used in modern Japanese urban and suburban rail rolling stock (the picture linked is of the new E235 series running on Tokyo's Yamanote Line).