My Hunter 20803 ceiling fan only works at one

The part you are making reference to is a capacitor and you can very likely get a replacement one at any local Radio Shack store. It is best to take the defective part with you so they can review all the markings to get the best replacment part you need.

If the capacitor isn't connected with wire nuts, you'll want to cut the wires as close to the capacitor as possible, so you'll have some wire to reconnect the new part. I also suggest you take a picture with your digital camera or camera phone BEFORE you remove the bad part, that way, you can refer back to it, when you are installing the new part.

With any electrical device, you will want to disconnect it from the power source before doing any repair or service work on it, to prevent electrical shock hazards. In the case of a ceiling fan, you can either remove the fan from the ceiling or turn off the breaker that provides power to that room (check to make certain you got the correct breaker turned off!) Also, you can make sure the wall switch that controls this fan, if you have one, is turned "off". You can tape over the switch to remind others not to turn it on, etc. while you get the parts to make the repair.

Hope you find this Very Helpful and best regards!