How to clear the screen correctly in ksh

Hello
In bash I can press Ctrl-l to clear the screen.
In ksh this key combination does not work. I can clear the screen only
using the command "clear".

How can I do this using hotkeys in ksh?
And how to do this when in vi mode?

I tried a workaround by assigning the key combination to Ctrl-l to cwm:
cat .cwmrc
unbind-key C-l
bind-key C-l "/usr/bin/clear"
After reloading cwm there is no effect.

-- 
Maksim Rodin