acf and meta

$meta_query = array(
	'relation' => 'AND',
	array(
		'key'     => 'acf_custom_field',
		'compare' => 'EXISTS',
	),
	array(
		'relation' => 'OR',
		array(
			'key'     => 'first_name',
			'value'   => '$search',
			'compare' => 'LIKE',
		),
		array(
			'key'     => 'last_name',
			'value'   => '$search',
			'compare' => 'LIKE',
		),
	),
);