Start with the Park Service's Civil War Soldiers and Sailors database. It's free and on-line; just do a Google search and you'll get there. It's not 100% accurate by any means but its pretty good and the easiest place to start IMO (oops ... don't generally like to post opinions but I've already gone off the cliff).
Next, also use Google to search for something like "Pennsylvania Civil War units" - there are many sites that have unit histories and lists of units from a given state or county within a state. You might get lucky (I have). It'll be easier, though, if you find the unit first.
If you find him and his unit, then you can get his war record either by contacting the Archives in Washington (there's a fee) or looking for one of the folks who will get the record for you and make digital files on a CD of all the pages (a great service, also IMO).
There may also be folks here who are familiar with the units from his county and can save you all that, but if they don't materialize try those steps.
Good luck in your search.