<?php
function change_search_query_var( $s )
{
if(isset($_GET['cmf']) && $s == null){
 	 $cmfterms = $_GET['cmf'];$sterm = array();
	foreach( $cmfterms as $k => $v){
	if($v['value'] =='wqsfcmfall'){$sterm[]= ''; }//no value for search for all custom meta, you can defined the value by urself
	$sterm[] = $v['value'];
	}

	$searchterm =  implode(",", $sterm);
	return $searchterm;

}
elseif(isset($_GET['s'])){

 $query = get_query_var( 's' );

      $query = esc_attr( $query );
     return $query;

}
}
add_filter( 'get_search_query', 'change_search_query_var', 20, 1 );


?>