CHAR vs TEXT args

I've created two PL/pgSQL functions with the same name and different
signatures:

CREATE FUNCTION ABC(CHAR) ...
CREATE FUNCTION ABC(TEXT) ....

I intended to call the CHAR-signature function like this:
SELECT ABC('R');

And the TEXT-signature function like this:
SELECT ABC('Right');

But I found that both calls invoke the TEXT-signature function.  So is
there any distinction between CHAR and TEXT?  Can I somehow specify
that the argument 'R' is to be treated as a CHAR, so the
CHAR-signature version of ABC is executed?

Thanks.
-David