wordpress $query->set to sort archive product pages, by *manipulated* ACF meta key value

I am trying to use the pre_get_posts action hook to sort products by ACF field for archive product pages.

The ACF field is a string, that contains characters and numeric value

My solution: to add missing leading zero's so that '040' < '180' will hold.

The following code is NOT working. What am I missing?

function sort_batteries_by_amper( $query ) {
        if( isset($query->query_vars['post_type']) && $query->query_vars['post_type'] == 'product' ) {
            $query->set('orderby', 'meta_value');    
            $query->set('meta_key', 'MY_KEY');    
            $query->set('order', 'ASC'); 
            $value = get_ah_value($query, 'MY_KEY'); // add leading zero's to int values < 100
            $query->set( 'meta_value', $value );
        }
        return $query;
    }

    add_action('pre_get_posts', 'sort_batteries_by_amper');

The following is a complete solution that works

add_action( 'woocommerce_product_query', 'ah_product_query' );
function ah_product_query( $q ) {
    if ( ! is_admin() ) { 
        $acffieldname = 'ACF_KEY_1';
        if ($q->queried_object->term_id == 320 || $q->queried_object->term_id == 321)
            $scffieldname = 'ACF_KEY_2';

        $value = get_ah_value($q, $acffieldname );
        $q->set( 'meta_query', array(
            array(
                'key'     => $acffieldname,
                'compare' => '>',
                'value'   => intval($value), 
                'type'    => 'numeric',
            )
        ) );
        $q->set('orderby', 'meta_value');    
        $q->set( 'order', 'ASC' ); 
    }
}

function get_ah_value($query, $s){
    if (!isset($query->query['p'])) return '';
    $str = get_field($s, $query->query['p']);
    if (empty($str)) return '';
    preg_match_all('/[0-9]+/', $str, $matches);
    $n = $matches[0][0];
    $s = intval($n) < 100 ? '0'.$n : $n;
    return $s;
}