I went over to look at my mom's furnace today to see if it had a "summer fan" switch. Her old one did but it was down in the crawl attached to the furnace. Access is through a closet floor hatch so it's not much harder than going down to a basement. Anyway, inspection showed they had net rewired a fan only switch or hooked it up to the tstat (dumb).
The furnace is working fine but I noticed when I had the cover off (no cut off switch for the cover which I found strange) that the "new" controller board she had to have installed 2 years ago has black burn marks in the PCB and one of the components looks fried. The furnace is 10 years old. 8 years doesn't seem like a very long life for a part that's a third of the cost of the furnace and to be scorched after only two years seems really bad. Is this a common issue? The replacement instructions were left inside the access panel (also doesn't seem wise) and it looks like Lennox buys these boards from White Rogers.