We have a heater/air conditioner combo (heater is in the house and the air conditioner unit is outside all runs through one thermostat air conidtioner works it kicks on and off but the blower fan on the inside of the house does not shut off. We replaced the thermostat and the limit switch on the units but the blower fan still does not shot off the only way we can shut it off is to trip the breaker does anyone have any thoughts on what else could be wrong

There is usually a fan relay that is sticking shut. On many units this relay is on a circuit board.

Is the thermostat blower control set to auto or is it ON. If on turn to auto.

Other than that you will have to trace the motor voltage back to see exactly what is causing it to stay on.