What happens to a VAC word when suffix with vowel is added?

It's difficult to answer your question without more context. "VAC" is not a recognized word in English, and it's unclear what you mean by "suffix with vowel."

Could you please clarify your question?

For example:

* Are you asking about a specific word that starts with "VAC"? If so, please provide the word.

* Are you asking about the general rules of adding vowels to words? If so, I can explain some common rules about suffixes and vowel sounds.

Once you provide more information, I can give you a more helpful answer.