Bit of background: The furnace blower originally did not not turn off at all (or if it did, very rarely did so), even when set temps were reached or when the system was off (fan setting is set to auto, not on). The AC unit outside would shut off when the set temp was reached, but the fan inside continued to blow. I called a technician, who said the issue was probably a bad fan switch relay and it was replaced.

Now the fan does turn off, but it doesn't appear to remain off. Even when the system is set to off, the fan randomly turns back on and off every 10-15 minutes. The technician reinspected it but said there's no apparent reason it should be doing this. As the fan doesn't turn on for a while after the system is off, he wasn't really able to verify that the fan was doing this. He replaced the relay again with a more "heavy duty" one, and just told me that even if just the blower is running, it shouldn't draw much power/create a high bill (my HVAC is all electric).

Is there any other reason it could be doing this? Is the relay still the problem? Or is this how they're supposed to operate (furnace/house is approx. 3 years old)? I had a much older home/hvac system before this and recently moved into this one so I'm not really familiar with the newer systems.

  • Is this blower also the source of fresh air? Perhaps the system is set to cycle every so often to make sure that you have X air changes per hour/day. Honestly though, I have a pretty limited knowledge of residential HVAC, it's just the first reason I can think of why your fan would want to intermittently run even without heating/cooling load.
    – JMac
    Commented Oct 6, 2017 at 15:05
  • Have you checked your thermostat settings and wiring? Some newer thermostats (e.g. my ecobee3) can be set to run the fan a minimum of X minutes per hour even when heat/AC are off. Also, can you post the brand/model of your furnace; it may have electrical configuration options that cause the fan to run a set amount. Commented Oct 6, 2017 at 15:24
  • To merge your guest and registered user accounts, select "Contact" at the bottom of the page, then "I need to merge user profiles" in the dropdown list. I've merged the two posts so you should be able to reply to the comments now.
    – Niall C.
    Commented Oct 6, 2017 at 20:56
  • Hope someone is still reading this, apologies for the late response. Make and model is Goodman aspf183016ea
    – user76281
    Commented Oct 13, 2017 at 23:17

2 Answers 2


Most furnaces I am familiar with have a thermocouple or timer switch that allows the fan to go into a cool down cycle before shutting off. I would start looking there.


Fresh Air Intake

Some HVAC systems provide the circulation for the fresh air intake system (The 'V' in HVAC). When operating in fresh air intake mode, these systems will periodically open the fresh air damper and turn on the blower of your central unit.

These systems are almost always controlled by an external Fresh Air Controller (Like this one)

Check around your HVAC system for the controller. They can be adjusted for how often and long they run, but it is presumed the current duty cycle selected is appropriate for your system.

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