A car's engine can begin to heat up quickly because as soon as the AC in on, heat is created in different ways. The engine having to work harder creates higher temperatures (if the AC compressor is bad) and the AC system creates heat that the condenser or water pump can't cool, also create higher temperatures.
Start by setting your air conditioner high
When trying to find the most reasonable setting for your air conditioner, you have to start somewhere. And, the best spot to do it at is 78 degrees Fahrenheit. According to Energy Star, it's an ideal temperature. 78 degrees keeps you fairly cool and comfortable during the day.
The amount of heat coming into the cooled space increases as the difference in temperature between the inside and outside increases. Therefore the total amount of heat being moved increases with the larger temperature differential. That means the AC will turn on more often to maintain the lower inside temperature.
If your air conditioner will turn on, and your thermostat is set properly, but your system is not cooling you may have a dirty or blocked air condenser. Your first step is to check the outside unit and clean around and remove any debris or weeds that are blocking air circulation.
In mild weather, a correctly sized and functioning AC will run in cycles of about fifteen minutes each. This is approximately two to three times per hour. If your air conditioner runs for less than ten minutes at a time instead, then it's probably oversized—too big for your home.