For my grow room, I've had good success with a portable 12,000 BTU air conditioner.
It's not a fancy split unit, but it gets the job done for my roughly 10x12 ft space, vented out a window.
I aim to keep my grow room pretty consistently in the 68-72F range.
When it starts creeping above 75F, I definitely notice issues with damping off and leggy growth.
Below 65F, germination can be slower.
Beyond using an air conditioner, I make sure there's still goo air circulation by using oscillating fans to keep the air moving and reduce fungal risk.
I also monitor humidity with a hygrometer.