The fan on my York furnace clicks when I attempt to turn it on. I changed the relay last week and it worked until this mornong but now nothing. Any ideas?

Test it at the leads to see if the voltage is getting to the motor.

If you have voltage at the motor and no motor running the motor is bad.

Make sure you have checked the run cap first that it has not popped because it will not start with out some assist.

video on how to check the voltage at the motor

https://www.youtube.com/watch?v=iVtpR2BekYM

If you have 0 voltage on a call for fan-on at the thermostat than the motor is not getting the voltage to start. You have to back up that route to see if you have a problem on the green thermostat wire, hi voltage wiring to the motor etc.