sounds like the ac clutch may be locked... to answer your question these ac units dont have serial numbers but rather part numbers, if your vehicle is a 2007 FOCUS(?ur title says fiesta) the part number is 4L3Z 19703 AC

i would check the ac operation visually befor you go and buy a compressor with someone outside looking at belt on engine have vehicle running and someone to turn ac on when ac comes on watch the belt by the compressor to see if compressor is spinning or not if it is not spinning and the belt is being spun over the ac pulley then a compressor will fix your issue but only temporarily plz report back