Nope, there's no weakness in the Climatact. Probably because without it Nami would to defenseless in a fight. Sadly, Nami is the Climtact's weakness and strength.
Of course, that every upgrade has to have a weakness. That is, unless that weakness makes the user invincible. Gears and Monster Chopper has weaknesses, but climatact, Kabuto, and Fire Leg aren't invincible upgrades.
For example, Sanji is still vulerable to attack (as much as he always is, at least) while using the fire leg.
The climatact it weak against wind, remember the wind blew the mirages away. In an extremly windy situation the climatact we not be vwery effective at all.