They sell cooling mats for dogs to lay on. They do not cost very much and would be a big help to a dog that does not have AC available to them.
Dog Beds: Cool Bed III at Drs. Foster & Smith
When it got quite hot here for a few weeks last summer I turned the AC on. I ended up having to put Gracie in her pajamas because she wanted to stay in her blanket all the time.
She prefers the warm weather but she is typical Yorkie and has no undercoat. I also am careful to keep her in shaded areas when we are outside. Dogs can also get sunburn, especially lighter haired dogs with parts down the middle of the back.