Changed rear pads and rotors on both sides, replaced passenger side caliper with refurbished one, bled the whole system including front brakes, now brake pedal goes to the floor, sytem is not leaking only thing I could come up with is the refurbished caliper is defective, any advice, please help...

 

Assuming that the bleeding was done properly (ie you kept brake fluid in the master cylinder reserve the whole time and you're sure all the air is out) and you are not leaking fluid . . . I'd have to say your brake booster/master cylinder is shot. Do you loose brake fluid over time? If not there is really no other explaination.