To be certain, you should:
* Consult a repair manual: A Chilton's or Haynes manual specific to your 1995 Chevy Astro van will show a diagram and precise location.
* Look at a diagram online: Searching for "1995 Chevy Astro oil pressure switch location" with images will often reveal helpful pictures.
* Use a flashlight and carefully examine the engine: Look near the oil filter; the switch is typically bolted directly to the engine block.
Be aware that some things may be different depending on the engine. Knowing your specific engine code will help refine your search.