。
The air conditioning is too strong, actually.
Literal
Air-conditioning [subject-が] is-working too-much [but-のですが].
~のですが ('it's just that..., actually...') is a soft, indirect way of raising a concern — literally closes a statement with an open 'but,' inviting the listener to respond. 効きすぎる combines 効く ('to be effective, work') + ~すぎる ('too much'). Typical polite register for making indirect complaints in Japan.