If you look on the aircon pump you should find a sticker with the manufacturer and model information on it.
Even if 2 pumps are the same extenally, that doesn't mean they are the insdie. Like a lot of components, aircon pumps tend to be made indipendant manufacturers (such as Sanden) who design and build pumps to suit a car manufacturers specification, to make it cost effective they produce series of pumps with common designs and a range of options to taylor them to applications. So even if pump from another car can be bolt on, the displacement or ports etc. may be different.