I am replacing my AC fan motor and the site recommends changing the capacitor at the same time. Do I need to do this or if my existing capacitor still works or should I just leave it? If I do need to replace it, the model # I currently have is no longer produced. Do I just get the capacitor that is recommended by the site where I am ordering the fan motor?

It's pretty much standard practice to replace the capacitor when you replace the motor. There's a good chance there is nothing wrong with the capacitor currently installed. When replacing a capacitor it has to be the same rating as the one being removed. If the store you're buying the motor from recommends a particular size capacitor your safe going with it.

The new one is Carrier 370V, 35/5 MFD and the old one is Dayton 440VAC, 40/5MFD. The motor model # is HC39GE237. The website I am purchaing the motor from said to use the Carrier capacitor listed above. The ratings don't seem to be the same. Should I do something different?

The new one is Carrier 370V, 35/5 MFD and the old one is Dayton 440VAC, 40/5MFD. The motor model # is HC39GE237. The website I am purchaing the motor from said to use the Carrier capacitor listed above. The ratings don't seem to be the same. Should I do something different?

These are dual capacitors, the 35 and forty signify the compressor side, and the 5 is for the fan. If you use the new cap, you will be using the wrong size for the compressor. Either keep the old cap and only use the herm (compressor side), and get a separate 5mfd for the fan, or get the correct dual cap which would be just like the old one, except it would be, well, new.
Now, that being said, if you actually had the old cap tested, and it is indeed within range, then you are probably safe reusing it. I always replace caps when changing motors, but that's because I have to warranty my work, and its just a good practice for a professional. Capacitors are fairly cheap and easy to replace. I have seen people replace a motor, only to find out it was just a five dollar cap that was bad. Now that hurts.

Thanks. I guess I ordered the wrong capacitor. It has not shipped yet, so I should be able to change it in the AM.