You said 'it runs but fan blades aren't spinning.'

Taking this "literally" - what it means is that the fan blade is 'loose' on the shaft of the motor. Look at the fan blade, the hub - in particular - and you will see where a 'set screw' should be.

If it's still there and 'loose,' all you have to do is 'tighten the screw' on the shaft of the motor (on the flat side).

If the screw is missing - you just need to find a screw that will fit the hole and replace it.

All of the above being said - it's also possible that you are hearing the compressor run and thinking the fan motor is running when in reality it's not. In the case that the fan motor is actually "not" running - then you have a completely different problem - the most likely problem being the fan motor is defective - in which case you will be out around $150 and up to replace it.

With the cost of window units today being fairly reasonable - you will probably be better off looking for a new unit.

Still, on the chance you have a simple problem, i.e. a burnt wire, or bad capacitor - it might be worth it to have a Service Tech take a look.

Hope this helps.

hope this helps