jQuery Grid Plugin - jqGrid

i'm starter in jqgrid, i write this code for build jqgrid in asp.net

var grid = $('#list');
            grid.jqGrid({
                url: 'jQGridHandler.ashx',
                postData: { ActionPage: 'CostTypes', Action: 'Fill' },
                ajaxGridOptions: { cache: false },
               direction: "rtl",

                datatype: 'json',

                height: 490,
                colNames: ['CostId', 'CostNo', 'CostName', 'Remark '],
                colModel: [
                        { name: 'COST_ID', width: 100, sortable: true, search:true, editable: false, hidden: true, key: true, index: 'COST_ID' },
                        { name: 'COST_NO', width: 100, sortable: true, editable: true },
                        { name: 'COST_NAME', width: 350, sortable: true, editable: true },
                        { name: 'REMARK', width: 300, sortable: true, editable: true }

                        ],
                gridview: true,
                rowNum: 30,
                rowList: [30, 60, 90],
                pager: '#pager',
                sortname: 'COST_ID',
                viewrecords: true,
                rownumbers: true
            });
           grid.jqGrid('navGrid', '#pager', { add: false, edit: false, del: true, search: true },
             {},
             {},
             { url: "JQGridHandler.ashx?ActionPage=CostTypes&Action=Delete", reloadAfterSubmit: false },
             { multipleSearch: true});
when click in search icon and show search box when enter text example 
costNo=1
 jqGrid not filter i think this action no work, please help me for implimet search in jqgrid
EDIT 01: when i add 
loadonce: true
 search work but when remove this option search don't work, please help me. thanks