[sdk8505]

A little history-
A couple of years ago we had trouble with this same thing. I had a guy come out and he showed me a burned relay. He bypassed the relay and the fan was left running continuously, which was fine. I paid him for the call and he said they would call me with a price for the relay since they had to order it. They would also come back and install it at no charge, except for the cost of the part. I got a call the next day and was told they could have the part in 2 days and it was $375, but installation was free. I know a little about electronic parts and I know this relay wasn't coming from a fighter jet, so that "free" installation was bull. I did some checking and the relay comes on a circuit board with other components and I could buy them all day long for less than $50. I cancelled the work order with the heating guy, bought the board and installed it, and everything has been fine.
Two years later this past Friday, we get the same smell, so I figure the relay is going again. I bypass the relay, order another one that will be in tomorrow, and everything is working fine for two days... no smell and the heat is working, but the fan is always on. Last night it drops to the 20's and we wake up to the smell again (maybe the drop in temperature and the smell is a coincidence?). I go to the furnace and I can smell it but nothing is melted (the first bad relay was starting to melt), nothing is hot, but the smell is there. I am stumped. I am reluctant to call another guy unless I really need to based on my previous experience. Any ideas? Thanks!