Some compressors require hard start kits to start up when using certain metering devices on the evap coil. (These are typically relegated to old style air conditioning units or in some cases very low end units that contain a piston style compressor.)

Hard starts come in various forms, there are different compressors (sizing) that in order to start properly need a start kit specifically matched as close as possible to the starting needs of that compressor.

If the start kit being used is a two wire, there is a better than even chance it will not work for long unless the kit (two wire) just happens to be the proper match for the compressor you are using it for. In some cases, the 2 wire start kit can kill the compressor in which it is attached to or the compressor kills the start kit (explodes)

I typically use a 3 wire kit, in which has a better probability as well as success rate of working. But these cost more and as you can imagine there is no guarantee these will be any more successful in all situations.

If a compressor is having a hard time starting, this is an indication of failure for the most part. So as to the success one will have or not have in regards to using hard start kit to assist start the compressor greatly depends on the level of failure the compressor has been exposed to. There is no metric to know this specifically.

In most cases a 'properly' fitted hard start kit can extend the life of an ailing compressor for many years. But there is also the risk that it will not work. It depends on a host of various factors.

Thanks, this was diagnosed by a tech. The units worked fine but wanted the hard start upgrade to extend the life of the units. Thank you again, great information!

I question why a 3 year old condenser needs a hard start kit. Perhaps the kit was unnecessary and caused a premature failure.

The unit was 'jarring' on and this helped with the noise. It would help with the compressor life so I thought it was a good idea, not required but since this is a low end unit, it didn't have it...

"Thanks, this was diagnosed by a tech."

Well if you are near Texas you probably replaced it or died of heat stroke by now. On the chance you haven't done anything yet,here's something easy to check. TURN THE POWER OFF. Follow wires from contactor and/or capacitor to where they connect to compressor. There's likely a cover that must be removed to expose connections. Look for badly corroded or burned connectors.