my central heat & ac blower motor turns on at random, usually 1 minute then off, sometimes again 1 minute later for about 1 minute, sometimes several minutes then off, it only circulates the air, no heat or AC because the thermostat is turned off, I recently changed the thermostat which has a jumper to work both heat & air, depending on thermostat settings, all worked well until the seasons changed, have any ideas. It's a 4 wire cheap thermostat, about $25.00