Ajax does not run correctly

I have a Ajax request that I make for my controller and it returns me a array with necessary data, however, the return of the request comes correct because giving a console.log(retorno) it shows me in the console the correct values , but it is somewhat unstable, hours it does the .html() function and has hours it does not, even returning the values correctly.

Ajax request code:

$j(document).ready(function(){
        $j.ajax({
            type: "POST",
            url: "<?php echo Mage::getUrl('fol_carousel/ajax/atualizaCarrinho') ?>",
            data:{

            },
            dataType: 'json',
            cache: false,
            beforeSend: function(){
            },
            success: function(retorno){
                //alert(retorno);
                console.log(retorno);
                //console.log(retorno['itensCarrinho']);
                $j('#cart-sidebar').html(retorno['produto']);
                if(retorno['itensCarrinho'] > 0){
                    console.log('Fez');
                    $j('.count-cart').html('<br/><br/>'+retorno['itensCarrinho']+'');
                }
                $j('.subtotal .label').html('Subtotal: R$'+retorno['subtotal']);
            },
            complete: function(){

            },
            error: function(x,y,z){
                alert(x);
                alert(y);
                alert(z);
                //alert("Erro!");
                /*window.location.reload();
                history.go(0);
                window.location.href = "{{store url=''}}";*/
            }
        });
    })

Code of my controller which requirement:

public function atualizaCarrinhoAction(){
            $cart = Mage::getModel('checkout/cart')->getQuote();
            $itensCart = Mage::helper('checkout/cart')->getSummaryCount();
            foreach ($cart->getAllVIsibleItems() as $item){
                $product = $item->getProduct();
                $id = $product->getId();
                $productName = $product->getName();
                $productPrice = number_format((float)$product->getFinalPrice(), 2, ',', '');
                $product = Mage::getModel('catalog/product')->load($id); 
                $productUrl = $item->getProduct()->getProductUrl();
                $image   = Mage::helper('catalog/image')->init($product, 'small_image')->resize(50);
                $media = (string) $image;
                $img = $media;
                $qty =  $item->getQty();

                $item = $cart->getItemByProduct($product);
                if ($item !== false) {
                    $id_quota = $item->getId();
                }
                $url_del = Mage::getUrl('checkout/cart/delete', array('id' => $id_quota))."form_key/".Mage::getSingleton('core/session')->getFormKey();

                $html['produto'].='<li class="item last odd">
                        <a href="'. $productUrl .'" title="'. $productName .'" class="product-image"><img src="'. $img .'" width="50" height="50" alt="'. $productName .'"></a>
                            <div class="product-details">
                                <a href="'. $url_del .'" title="Excluir Este Produto" onclick="return confirm("Deseja realmente retirar este produto do seu carrinho?");" class="btn-remove">Excluir Este Produto</a>
                                <a href="" title="Editar produto" class="btn-edit">Editar produto</a>
                                <p class="product-name"><a href="'. $productUrl .'">'. $productName .'</a></p>
                                <strong>'. $qty .'</strong> x <span class="price">R$'. $productPrice .'</span></div>
                        </li>';
            }
            $html['itensCarrinho'] = $itensCart;
            //Pegando o SubTotal do carrinho
            $subtotal = Mage::helper('checkout/cart')->getQuote()->getSubtotal();
            $subtotalCart = number_format((float)$subtotal, 2, ',', '');
            $html['subtotal'] = $subtotalCart;

            echo json_encode($html);
        }