I have a Ruud Deluxe 80 plus furnace. It's just over 20 years old. Model # UGLC-07ECBGS. The blower keeps running even though there is no heat. It is intermitent. I can shut the furnace off and on again at the breaker and it may not do it for a while. Is it the Blower relay/switch? If so, how do I identify it?