Ajax :: Redirect To URL Response Not Working

I have a simple ajax request that is supposed to (after a short timeout) redirect the page to the URL that the server sends back but it just wont work. It does work without the setTimeOut() function however.

var http = false;
if(navigator.appName == "Microsoft Internet Explorer") {
http = new ActiveXObject("Microsoft.XMLHTTP");
} else {
http = new XMLHttpRequest();
}

function go() {
var u = "http://site.com/";
http.open("GET", "go.php?" + "u=" + u, true);
http.onreadystatechange=function() {
if(http.readyState == 4) {
var redirURL = http.responseText;
setTimeout("window.location.href = redirURL;" , 2000);
} }
http.send(null);
}