It used to be “ac y mae” as I understand 
Edited to add this-
here’s an earlier thread on the same question -
Ac before consonant in “ac mae”? - Welsh / General / Questions - SSi Forum (saysomethingin.com)
It used to be “ac y mae” as I understand
Edited to add this-
here’s an earlier thread on the same question -
Ac before consonant in “ac mae”? - Welsh / General / Questions - SSi Forum (saysomethingin.com)