I've read about blowers (heat pump) that won't shut off, no matter what done to thermostat, and the cause typically being a faulty control board, and/or fan relay on contl. Board. I replaced board, as tech removed green wire to demonstrate it's fault (didn't turn blower off), but tried a brand new cont'l. Bd. And no change. Could it be Limit Switch? I can see no limit switch anywhere. Where could it be on a Payne heat pump?