Many of us consider furnace repairs to be needed because of a catastrophic failure such as an air handler motor being burnt out or a malfunctioning burner assembly. Although these issues can happen, you may be surprised to know that some of the most common furnace repair issues are actually caused by small issues. For example, your air filters can have a massive impact on performance and could be the underlying reason for your repair issues. 
The Air Filter Basics:
While the air filter may seem to be an unobtrusive part of your air conditioning system, it is a vital component. Your ductwork is likely to be filled with dust, dirt and debris that can not only compromise your air quality, but can cause issues if they enter the furnace. The air filters are designed to prevent this and protect your system. Air filters are usually installed in the air return ductwork of the furnace. They are designed to protect the system from any debris or particles that could blow in from the ductwork.
Filters have a relatively simple construction; they are simply a fiber mesh screen over a frame. As air flows through the filter, it captures any particles, preventing them from uninhibited flow through the system. Unfortunately, once the particles are trapped, there is no way for the filter to get rid of the debris. The filters require manual cleaning or replacement to prevent them from being clogged. Most manufacturers recommend changing filters approximately every ten to twelve weeks.
Dirty Filters and Short Cycling:
If you are a little lax about cleaning or changing your filters, you could end up with your system short cycling. A dirty filter restricts and blocks airflow to the furnace, which can be the beginning of a real problem. When the airflow is restricted, heat is trapped inside the HVAC system. This issue causes the furnace to overheat, which can activate the limit switch. The limit switch is a safety measure, which allows the system to be shut down in the event of a problem. Unfortunately, the switch cannot address the underlying problem, so it merely allows the furnace time to cool down. Once the furnace temperature drops, it will start again, and the overheating will happen again. This cycle of switching on and off can continue indefinitely, and is referred to by HVAC professionals as “short cycling”. The main danger of short cycling is that it creates additional strain on the system that the furnace is not designed to handle. Short cycling can not only mean that your energy usage increases, but it can compromise the lifespan of your equipment.
Detecting the Problem:
The average HVAC system has approximately three to six on-off cycles per hour. When your system is short cycling, this number can increase significantly. This means that you will be able to tell if your system is short cycling, simply by counting the number of times the system stops and restarts in an hour. If your system is short cycling, it is a good idea to switch it off and call for professional assistance. A trained and experienced technician will be able to assess your system and quickly trace the source of the problem.