var chc;

function changeCityFrame(site_url, ret_page) {

    if(!chc)
        chc = document.getElementById('chooseCityList');

    if(nybl = document.getElementById('ny_bl')){
      nybl.style.display = 'none';  
    }
    inf = document.getElementById('ajaxInfo');
    inf.innerHTML = 'загрузка...';inf.style.display='block';
    chc.style.display='block';
    chc.innerHTML='<iframe src="' +  site_url + 'dc/city_choose.php?return=' + ret_page + '" frameborder=0 id="chCityFrame"></iframe>';
}