Facets display values instead of labels
try in search API > your index > search your field and then in the column type, select STRING.

Also maybe you can hook your field:

function HOOK_facet_items_alter(&amp;$build, &amp;$settings) {
   if ($settings-&gt;facet == "YOUR_FACET_NAME") {
       foreach($build as $key =&gt; $item) {
          $build[$key]["#markup"] = drupal_strtoupper($item["#markup"]);
        }
    }
}