When the fan of your HVAC system runs continuously, it could be one of two things. The first is that someone set the thermostat to “On,” causing the fan to run continuously. Try setting it on “Auto.” The fan should start turning on and off as usual. If that doesn’t happen, then you may have a problem with the HVAC blower.

Before you call for professional help, there’s one more thing to try: Look for the fan-limit switch, inside the furnace-panel cover, which is usually in the upper-righthand corner. This switch turns the HVAC blower on and off at the right times. When the switch is working as it should, the furnace fan should turn on just a few minutes after the heat turns on, and then the fan should turn off a few minutes after heating is done. If the fan keeps running, then the furnace fan-limit switch could be set to manual.

The fan limit switch should have a small white button, located on the lower-left corner. This button is what sends the command for the switch to operate manually — which means the fan runs all the time — or automatically — which means it only runs during heating cycles.

If the button is pushed in, then it’s set to “Manual” and is telling the fan to keep running. Reset it to “Auto.”

There could be a couple of things going on here:

  1. The fan-limit switch is faulty and needs to be replaced.
  2. The thermostat wiring is bad.

If there is a malfunction, you will need to call for repairs.

Should You Allow the HVAC Blower to Run Continuously?

Some homeowners like to turn the fan to “On” so it will run continuously. They don’t like the fan turning on and off, perhaps because of the noise. But also, when the fan runs, the system can clear out airborne pollutants better. However, running the fan continuously will make it wear out faster.

For more on the HVAC blower, contact Mowery Heating, Cooling and Plumbing. We serve Indianapolis and the surrounding area.