When should you have your HVAC units checked?

When should you have your HVAC units checked? I have been heavily considering starting to get our HVAC units checked right now.

I am just sleepy of having so several problems with our HVAC units.

I don’t understand why our HVAC units are constantly having trouble. I think that our gas furnace plus our central air conditioner system are old, however I don’t think that they should be having this much trouble. Honestly, I don’t want to complain about our HVAC units. I understand that HVAC units aren’t’ made to last forever, plus I don’t mind spending money on our HVAC units. My HVAC units are absolutely pressing, plus I wouldn’t be able to survive without them. Since our HVAC units are so pressing, plus I am not frustrated about investing in our HVAC units. However, our HVAC units constantly seem to cut down at the worst time… During the hottest day of the summer, our central air conditioner system will swiftly stop toiling. During the coldest tonight of winter, our gas furnace will swiftly stop toiling. I have no system what is wrong with our HVAC units, however they cut all of the time. However, if I could have an HVAC professional look over our HVAC units plus have them maintenance the problems before I need the HVAC units, it would be so much better. I heard that you can pay an HVAC professional to perform these HVAC inspections, plus I system to call them. However, I want to think how often you need these HVAC inspections. I am assuming that you would do them once in the fall plus once in the Spring. That would make the most sense with the HVAC units. What do you think?
Heating maintenance