wordpress file upload with ajax when site is ajaxyfi

I am getting problem in upload any file. My word press site is using Ajax Page Loader Plugin.So page is not refreshing when the form is submitting..

I am not getting any value in PHP code in functions.php in print_r($_FILES);
But i am printing any string with echo(); it is printing but why print_r($_FILES); is not getting any value.

HTML form

<form id="career_form" name="career_form" enctype="multipart/form-data">
    <span id='errfrmMsg' style='margin:0 auto;'></span>
    Upload : <input id="career_resume" class="field" style="height: 25px;" type="file" name="career_resume" multiple /></td>
    <input type="hidden" name="action" value="career" />
    <input id="submit_button" onclick="submit_career();" type="button" value="Send" />
</form>

j Query

function submit_career()
{
    jQuery.post(the_ajax_career.ajaxurl_career,
        jQuery("#career_form").serialize(),
            function(response_from_the_action_function){
                jQuery("#errfrmMsg").html(response_from_the_action_function).css({"display":"block"});
            }
        );
}

Php code in functions.php

wp_register_script("ajax-career", get_bloginfo('template_directory')."/js/custom_js.js", array( "jquery"));
    wp_enqueue_script('ajax-career');
    wp_localize_script("ajax-career","the_ajax_career", array("ajaxurl_career" => admin_url("admin-ajax.php")));
    // add actions
    add_action( "wp_ajax_career", "ajax_action_career" );
    add_action( "wp_ajax_nopriv_career", "ajax_action_career" );

    function ajax_action_career(){ 

        //Nothing getting in this print_r($_FILES) function;

        foreach ($_FILES["career_resume"]["error"] as $key => $error) {
            if ($error == UPLOAD_ERR_OK) {
                $name = $_FILES["career_resume"]["name"][$key];
                move_uploaded_file( $_FILES["career_resume"]["tmp_name"][$key], "uploads/" . $_FILES['career_resume']['name'][$key]);
            }
        }
    }