My house has a York brand central heat and air that's about 3 years old. For some reason on really hot days the outside unit will come on but the fan will not turn. Sometimes if you bump the thermostat down a few degrees the fan might kick on. I have had the fan replaced with a new one but it continues to do the same thing. Any help would greatly be appreciated.

Check the wiring to the fan motor. Next check any controls for the fan that might be in the unit.

When the fan is not running you need to see if there is voltage going to the motor. It is also possible that the fan motor capacitor is defective.

Try turning the fan switch to on at the thermostat when you notice the blower not coming on, if the blower runs it may be in the thermostat not giving the blower 24v to run in cooling mode. The problem can be in the thermostat,control board and or more.