I have a Goodman Airhandler Split Unit and my blower on one of the units will not cut off. I have changed the relay switch on both units. Switched the thermostats around and still it will not cut off. I can turn the thermostat off and it will constantly blow. I have to cut the main breaker off just to cut the one unit off. It will heat and cool but will not cut off. Please help!

Your problem is in the blower control circuit since that is the only item that controls the blower with the exception of a heat style air handler and then the sequencer can short the blower control terminals and cause the blower to run all the time. This happens with these no model number units.