Switching the library's HVAC system from AC to heat or from heat to AC is quite a large operation for the library building and each is only done once per year.
The College waits until there is some surety that the weather will remain cold or warm; otherwise, if the weather gets cold or warm again and the heat or AC has been turned on, the building becomes unbearably hot or cold.
It's always a good idea to dress in layers (that's what the librarians do!), and check different areas in the library. It can be warmer or cooler depending where you are.