Adding AC to existing furnace. Need Return air ducted?

[twoply]

A resident is adding AC to a furnace. The return air ducts are stubbed out into the basement and not tied into the furnace.
Do the return air ducts need to be tied into the system now?
And which code section says so?

I have my answer, but I have a challenger....

Thanks y'all!

 

[mtlogcabin]

yes if the furnace is fuel fired and not a direct vent appliance
M1602.2 2012 IRC