Here you can find the instructions in how to to enable Price slider option for Category Page.
Price Slider provides your store visitors with the opportunity to filter products by certain price range without reloading the Catalog Page.
1. Log into Magento admin.
2. On the Admin sidebar, tap Stores and choose Configuration under the Settings section.
3. Then navigate to TemplateMonster > Catalog Ajax in the left side menu.
3. Move to the Price slider option and select “Enable” from the option dropdown.
4. Press the Save Config button.
5. Clear the Magento cache.