$(document).ready(function() {

    $("select[id$='ddlSearchStates']").change(function(event) {
        SetCityMode();
    });

    $("input[id$='txtSearchZip']").keydown(function(event) {
        SetZipMode();
    });

    $("input[id$='txtSearchCity']").keydown(function(event) {
        SetCityMode();
    });

});

function ValidateSearchCriteria(sender, args) {
    var ctlZipcodeTextBox = $("input[id$='txtSearchZip']");
    var ctlStatesDropbox = $("select[id$='ddlSearchStates']");

    if ((ctlZipcodeTextBox.val() == "" || ctlZipcodeTextBox.val() == undefined) &&   (ctlStatesDropbox.val() == "Select" || ctlStatesDropbox.val() == undefined)) 
    {
        args.IsValid = false;
    }
    else {
        args.IsValid = true;
    }
}

function SetCityMode() 
{
    $("input[id$='txtSearchZip']").val("");
}

function SetZipMode() {
    $("input[id$='txtSearchCity']").val("");
    $("select[id$='ddlSearchStates']").val("Select");
}