Why does my AC or heater keep going off and on?

When temperatures dip low and it’s time to turn on the furnace for the season, the last thing you need is the nasty surprise of a malfunctioning HVAC unit. Most of the time they just work in background and we don’t even think about them… until they start acting up! One questions we get from time to time is “Why does my AC or heater keep going off and on?”

When things do malfunction, though, you will take notice. One thing that often goes wrong with a unit is frequent short-cycling. You will notice this when your furnace keeps turning on and off more frequently than normal. Pay attention when you notice this because if you address it early on in the problem, it is a much easier and cheaper fix than if you let it go and it causes more damage.

When in use on a very cold day, a furnace should cycle on and off between 3 and 6 times per hour. Pay attention to how long it stays on, rather than how often it turns off. It should stay on for several minutes at a time – if not, it is time to evaluate the following list of common causes of a furnace that frequently turns on and off:

Dirty Air Filter

The filter might be dirty. Check and change the filter. Running your furnace with a dirty filter is the most common cause of malfunctions. It can restrict airflow and damage the coils. Prevent problems by replacing on a regular basis.

Location of your thermostat

The location of your home’s main thermostat may not be ideal. Your thermostat tells the HVAC when to turn on and off. If your thermostat is located next to a vent or window, it will read the temperature of the air around it, and makes the furnace think the home is colder or warmer than it is. Call a technician to relocate the thermostat.

Your HVAC unit is the wrong size for your home

Your system might be too big for your home. If you have a newer home or have had the unit replaced, but it is too big for your square footage, it will heat too rapidly and your furnace will frequently turn on and off. It also makes for a bigger energy bill and shortens the lifespan of the unit.

A furnace that keeps turning on and off is a cry for help from your HVAC unit. Give it a little attention now and it will pay huge dividends in the end with a comfortable, worry-free winter.

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