cornstar wrote:OK, thanks nwaelder!
Just so you know what I have here, it's a new LMF 100K furnace.
My first question is why does the room air fan come on for 30 seconds and stay off for 90 seconds?
LMF uses disc type temperature switches in the plenum. About a year ago they changed to a "rod" that had the three temp discs mounted on it. This change was done to allow easier service. Initially, the placement of this rod in the plenum was not optimal, and this caused the blower to cycle excessively. So, I suspect that you may have an earlier unit with a sub-optimal modification. Call LMF and they can give you the details of how to position the probe assembly in the correct location. I'd tell you, but I don't know the details.