My outside AC unit (14 years old) was not working correctly - the compressor was not coming on, and the fan required me to push it to get it going.  These symptoms are usually associated with a bad capacitor, and I ordered a new one.  I also found out about this product, which gives existing capacitors extra power on startup, so I ordered this as well.  The hard start relay came first, so I hooked it up to my old capacitor, and just this addition was able to get everything working.  When my new capacitor arrived, I installed that, and kept the hard start relay hooked up.  My AC unit fires right up, just like it was brand-new, and everything is working as well as it did when it was brand-new.  Although I technically did not need this hard-start relay, but I think that leaving it in will extend the life of the capacitor by helping ouyt with teh compressor startup (which puts the most strain on the capacitor.  overall, I'm very happy with the product, and saved thousands of dollars by not having to buy a new AC unit.