This will be our second year with our little yorkie. Our summer temps are often high 90s and low 100s. The one thing we don't have is high humidity.
We found several issues in the heat. Inside our pup was given a temperature controlled area. We found if the room is warmer that high 70s, it starts to feel too warm because the pup isn't used to it. They always need access to water. She didn't want or require as much bedding available. We also kept her a little shorter trim.
Outside is a big deal. Even in the car with the air conditioning on she had to be out of the direct sun coming in a window. So we used shades just like for a baby. She also needed frequent water breaks. We put a thermometer in the car to remind us out hot the car can get. The dog can not be left in the car, even with the windows rolled down a little bit. When it's 100 degrees out, that's the ambient air temperature not the temperature in the direct sun, which would be much hotter. So thinking you can park the car in the shade with the window cracked? The air coming in is 100 degrees!! Sidewalks, pavement, everything is too hot.
Here is an article that gives a lot of information. They also have cooling products for dogs.
Yorkshire Terrier Summer Care