Why would the central air contintioning unit continue to run when the inside thermostatat is shut off?

I suspect that your outside unit is not running and that it is your blower only that is running. This could be caused by a sensor that actiaves the blower when the heat exchange is heated for the heating of your home. If it is warm enough and/or you have a standing pilot the sensor will make the blower run. Also, some units have a switch on them that can be set so that the blower runs all the time as well as the switch that your thermostat may have. One of the switchs may have been filp or bump to on.