diablo9999

Hi there I need your help please, got a big problem, my ac is working on the highest speed only, it was working on 3 speeds like 6 months ago, but the lower ones just quit working, the automatic control unit works fine, but as soon as it changes to lowers speeds it just stop blowing, it blows very cold, I tried changing the ac unit control but didn't work, do you have any ideas what is causing this, or what is the fix? thanks.