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// change 'rebate' to your post type

function sort_rebate_archive_query( $query ) {
  #var_export($query);
  if ( is_admin() || !$query->is_main_query() )
	return;

  if ( is_post_type_archive( 'rebate' ) ) {
	$query->set( 'posts_per_page', 40 );
	#$query->set( 'orderby', 'title' );
	#$query->set( 'order', 'ASC' );
	return;
  }

  if ( is_tax('business') ) {
	$query->set( 'posts_per_page', 20 );
	return;
  }

  if ( is_tax('residential') ) {
	$query->set( 'posts_per_page', 20 );
	return;
  }
}
add_action( 'pre_get_posts', 'sort_rebate_archive_query' );