HEllo, I recently had a new fan motor installed in my central air unit. My unit is over 20 yrs old. It has always had one compacitor. The tech put an extra compacitor on the unit he said to run separate with the compressor. Is he doing this because the fan motor he installed is to small, and he just not telling me?

No, he did that because it is recommended that a new capicitor be installed with a new motor this warrantys that he won`t have to come back later and charge you another service call because the split capicitor that was already in your unit is old and won`t last very long with the new motor, now all the old capicitor has to do is start the compressor only,therefore will last longer

And besides that chances are the low side of the older capicitor probably doesn`t match what the new motor calls for