Edit: I just posted this same question, but did so as a guest. I then created a new account (same name), but now am unable to reply to comments on it because its technically not my post.
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.