Doing Your Part to Keep Your HVAC System Running

A few months ago, my air conditioner completely died. I woke up in the middle of the night covered in sweat, and I didn't know what to do. The next day, I called an HVAC expert, and they came out to inspect my system. It turned out that it had failed because of filthy filters and a clogged return duct, which made me sick to my stomach. I had caused the problem, and I needed to learn how to fix things. My HVAC professional taught me a few easy maintenance techniques that I didn't know before, so that I could maintain my new system. Check out this blog to learn more about HVAC yourself.

Signs Your Furnace Fan Limit Switch Needs to Be Cleaned or Replaced


If your furnace isn't keeping you warm enough, the problem might be the fan limit switch. This is a small part that is important for triggering the blower to turn on and off at the right time.

Other things can cause your furnace to malfunction too, so the furnace repair technician has to test the limit switch with a multimeter to see if it's bad. Here are signs the switch could be malfunctioning, why it goes bad, and how a furnace repair technician fixes a bad limit switch.

Signs of a Malfunctioning Limit Switch

The fan limit switch in your furnace has two jobs. One is to monitor the temperature in the furnace and turn the blower fan on and off according to the temperature. Another function is to monitor for excessive heat and shut the furnace down if it gets too hot.

When the switch has a malfunction, it might not turn the blower on when it's supposed to. That would cause the blower fan to stay idle and not blow warm air through the ducts. Another possibility is that the switch wouldn't turn off the fan when the high temperature is reached. If this causes your furnace to get too hot, your furnace could shut down and not come back on at all until it has been checked and reset by a furnace repair technician.

Causes of a Limit Switch Malfunction

Poor airflow is the primary cause of trouble with the fan limit switch. Low airflow can be caused by a filter that's matted with dust, blocked ducts, or a blower that's so dusty it can't create enough airflow.

Reduced airflow causes the limit switch to overwork and break down. When the furnace repair technician comes to fix the limit switch, they should also look for the cause of the failure and repair it so the new switch doesn't start malfunctioning too.

Repairs for a Bad Switch

A malfunctioning limit switch can be cleaned or replaced depending on what's wrong with it. If the switch is just dirty, the furnace repair technician can remove it from the furnace and clean it thoroughly, being careful about how and where to touch the switch so it isn't damaged. A dirty switch can malfunction, so cleaning might be a quick and easy solution.

If the furnace repair technician tests the switch with a multimeter and determines that it's bad, the switch has to be replaced with a new one. This is a straightforward job since the switch is easy to reach and replace.


1 March 2022