Hi, Sometime the unit runs fine. Mostly it short cycles or runs OK and then after it comes on within an 1/2 hour or so the blower keeps running with red lite on, no heat. Cleaned flame sensor. Checked igniter ohmed out at 68.7 +. Pressure switch OK. What happened, I turned April air humidifier water on, and cleaned air conditioner drain that when rust fell in the furnace while in was running that's when all the problems started?? What is reverse polarity, could that fine rust do that so something?? Please Help if you can. Thank you RRM Rich [email protected]

Not likely reverse polarity, unless you removed some wires and then reattached. When you say short cycles do you mean it heat and shuts off normally? Or are you getting flame failure code?