Though Corsica is a small island, 183km long and 84km wide (114 by 52 miles), there are regional changes in its temperature and climate based on altitude and wind exposure, with altitude variations from sea level to about 2,700 m (9,000 feet). In general, the south side of Corsica is warmer than the north.
Because of its Mediterranean location, the weather in Corsica is usually sunny and pleasant with clear blue skies from April through October and very little rain fall. Cooling winds in the summer provide a refreshing break in the evening.
When hiking in the mountains, even in the hot summer months, one must always wear a jacket and use a sleeping bag. It is important to be protected and prepared for any sudden changes in weather at any time regardless of season.
From November to April many hotels and restaurants shut down and only a few remain open. Spring is a wonderful time to visit when wild flowers can be seen blooming everywhere and there’s still snow on the mountains.
Except for the months of July and August, air conditioner is not essential not even in areas near the beach. The rooms at the Club Med village in Cargèse do not have A/C. (When I stayed in Club Med in the month of September I had to shut down the windows every morning because of the cool air coming in the room). The weather is generally mild during spring and fall and even winters aren’t really that cold.
In Corsica most homes (and many hotels) are not equipped with air conditioner and only use ceiling fans. Heating is available for use during the winter months.
Unless you plan to arrive in Corsica during peak season, (July-August), when booking a hotel or holiday residence air conditioner (la climatisation) should not be a big concern.