Passing Data From Controller To View Using JSon Object

I have the following to get the Json abject passed from the controller and populate the various textboxes in the view. However, nothing is happening even though controller is passing a valid Json object. What is wrong with this code?

<script language="javascript" type="text/javascript">
$(document).ready(function() {
var url = '<%=Url.Action("DropDownChange") %>';
$("#vendorID").change(function() {
var selectedID = $(this).val();
if (selectedID != "New Vendor Id") {
//$.post('Url.Action("DropDownChange","Refunds")', function(result) {
$.post(url, { dropdownValue: selectedID }, function(result) {
alert(selectedID);
$("#name").val(result.Name);
$("#city").val(result.City);
$("#contact").val(result.Contact);
$("#address2").val(result.Address2);
$("#address1").val(result.Address1);
$("#state").val(result.State);
$("#zip").val(result.Zip);
});
}
});
});
This is the code in my controller;
public JsonResult DropDownChange(string dropdownValue)
// This action method gets called via an ajax request
{
if (dropdownValue != null && Request.IsAjaxRequest() == true)
{
paymentApplicationRefund =
cPaymentRepository.PayableEntity(dropdownValue);
paymentApplicationRefund.Address1.Trim();
paymentApplicationRefund.Address2.Trim();
paymentApplicationRefund.Name.Trim();
paymentApplicationRefund.City.Trim();
paymentApplicationRefund.Contact.Trim();
paymentApplicationRefund.State.Trim();
paymentApplicationRefund.Zip.Trim();
return Json(paymentApplicationRefund,"application/json");
}
else
{
return null;
}
}