My thermostat and furnace blower fan work perfectly in the AC mode, but when I turn the setting to HEAT, the heating elements come on and I hear the relay click, but the blower fan will not come on until I reset the thermostat to the ON position. After the heater has been on for awhile, if I turn it back to AUTO, the fans shuts off, The thermostat was replaced about a year ago for this problem, but it did not fix the problem. The old thermostat was a Hunter didgital and it was changed out with a Honeywell.