# How do you know enough freon is in your home central ac by monitoring the temperature flowing out of the air duct and what temperatures are correct for the outside temperature?

Check the superheat in the system.

### Why is doubling the Celsius temperature a good approximation?

The equation for working out the temperature in fahrenheit from celsius is f = 9c/5 + 32 In other words, you multiply by slightly less than two, and then add more on. Therefore for many temperatures, just doubling would be a good approximation. Indeed, when the temperature is 160celsius, doubling would be correct.