Hard to say really, it could be that there is some debris between the clutch and stator OR your clutch may be worn out and the friction material may have deteroated. You might want to pull the front of the clutch off to inspect it to see what you have, this won’t disturb the AC charge so you don’t have to worry about that but watch out for any shims that might fall out and make sure to put them back if they do. Good luck.