hi you use void please replace with actionresult.
public ActionResult Search(string filter)
{
List<sb_detail> dets = db.SB_Details.ToList();
if(filter != null)
{
dets = dets.Where(d=>d.SB_Model.ToUpper() == filter.ToUpper());
}
RedirectToAction("SearchResults", "Home", new {details = dets});
}