Custom posts type with custom taxonomy wp_query

I having some difficulty figuring out how to query a custom post type in a specific (custom) category..

So far I have the following code in my functions.php

function post_type_discog() {

	register_post_type('discography',
		array(
	  	'labels' => array(
				'name' => __( 'Discography' ),
				'singular_name' => __( 'Discography' ),
				'add_new' => __( 'Add New' ),
				'add_new_item' => __( 'Add New Discography' ),
				'edit' => __( 'Edit' ),
				'edit_item' => __( 'Edit Discography' ),
				'new_item' => __( 'New Discography' ),
				'view' => __( 'View Discography' ),
				'view_item' => __( 'View Discography' ),
				'search_items' => __( 'Search Discographys' ),
				'not_found' => __( 'No Discographys found' ),
				'not_found_in_trash' => __( 'No Discographys found in Trash' ),
				'parent' => __( 'Parent Discography' ),
			),
      'public' => true,
      'show_ui' => true,
			'exclude_from_search' => true,
			'hierarchical' => true,
			'supports' => array( 'title', 'editor', 'thumbnail' ),
			'query_var' => true
			)
	  );
	}
	add_action('init', 'post_type_discog');

	add_action( 'init', 'create_discog_taxonomies', 0 );

	function create_discog_taxonomies()
	{
	  // Add new taxonomy, make it hierarchical (like categories)
	  $labels = array(
	    'name' => _x( 'Recordings', 'taxonomy general name' ),
	    'singular_name' => _x( 'Recording', 'taxonomy singular name' ),
	    'search_items' =>  __( 'Search Recordings' ),
	    'popular_items' => __( 'Popular Recordings' ),
	    'all_items' => __( 'All Recordings' ),
	    'parent_item' => __( 'Parent Recording' ),
	    'parent_item_colon' => __( 'Parent Recording:' ),
	    'edit_item' => __( 'Edit Recording' ),
	    'update_item' => __( 'Update Recording' ),
	    'add_new_item' => __( 'Add New Recording' ),
	    'new_item_name' => __( 'New Recording Name' ),
	  );
	  register_taxonomy('recordings',array('discography'), array(
	    'hierarchical' => true,
	    'labels' => $labels,
	    'show_ui' => true,
	    'query_var' => true,
	    'rewrite' => array( 'slug' => 'recordings' ),
	  ));
	}

Which works great (on the surface at least!). I can create a custom post type (which I can retrieve with WP_Query like so:

<?php
				$new = new WP_Query('post_type=discography');
				while ($new->have_posts()) : $new->the_post();
					the_content();
				endwhile;
			?>

But if I add a category I can’t seem to filter my results as I normally would, by adding:

category_name="my-category"

to the WP_Query $new = new WP_Query('post_type=discography&category_name=my-category');

This won’t display anything! I’ve tried renaming ‘category_name’ to ‘recordings_name’, but then it just displays all the entries in that custom post type.

Interestingly enough, I have been able to filter my results by customs tags but I don’t see why I can’t get it to work with custom categories!

Help!