When our technicians go out on service calls, one of the common questions asked is when should I have my HVAC maintenance service.
The answer is twice a year. One visit for air conditioning and one visit for heating. You should have both checked before you need to use them.
Preferably early spring and early fall. Please consider heating inspections more important because of the dangers from fire and carbon monoxide inhalation. Air conditioner and furnace inspections are also very important because of the cost involved in operating and replacing these systems.
If there are loose wires, bad parts, dirty coils, dirty filters, low Freon etc. The heating and air conditioning system may still operate, with the above mentioned problems in low load conditions but when it gets warmer or colder outside it is likely that the system will break down. This causes a very heavy strain on the systems major parts.
Straining your heating and air conditioning equipment by operating it in such conditions will shorten its life span and cost you money over the long run. Just one loose wire or not changing your air filter can potentially cost you thousands of dollars and leave you without heating or air conditioning for several days.