SEARCH CHARSET command with special character in IMAP

How can I find email with the subject ã, or á, é, à? Special symbols.
I used the command:

c: A05 SEARCH CHARSET ISO-8859-1 TEXT {6}
s: +go ahead
c: ã
s: * SEARCH
s: A05 OK SEARCH completed (Success)

but i have an email with the subject ã in my inbox