I have a central heat and air unit, its not a heat pump, it does not switch on properly if the thermostat is set at 72 it won't turn on until it is well below 60 degrees then only runs for a little while and does not reach selected temp. it I turn it off then back on to auto it will ryan for a while if the temp is lower than the selected. I have changed the thermostat 4 separate times and it is wired correctly I just put in a brand new honeywell thermostat and no difference in the problem. Anyone have any ideas