I live in an area where we have very unpredictable weather.
You are never sure when it is going to be summer or winter.
We can go for a couple weeks with absolutely beautiful weather. I mean, you don’t need to have either a furnace or air conditioning. One morning you wake up to snow and ice, and you know winter is upon you. You rush to get some heat in the house before your toes freeze. In spring, you’ll be enjoying a couple of weeks of really nice weather and then the temperatures begin to rise. A couple days later, it is snowing again. My wife starts harping on getting the air conditioning service done, as soon as the calendar says it is spring. I call the HVAC company to make her happy. I don’t know when summer is actually going to arrive, so calling the HVAC company is always a good idea. I’ve found that determining when to turn on the air conditioning unit has nothing to do with the date on the calendar, but everything to do with the weather. I like to wait to call the HVAC company when I know the furnace is no longer needed. I can’t have the service done on the air conditioner and also have the furnace cleaned at the same time. The furnace works so much longer and harder than the air conditioning unit, that I want to make sure it is cleaned and checked after it has been used. I may change the air filter every month, but it doesn’t hurt to give the furnace a bit of extra care since it does such a good job for us.