here is a little long lost info on hardstart kits. every manufacturing company offers them if you look on the wiring diagrams but they offer it as an option, leaving it up to the person to who installed it to decide if it needs to be put on.
this is what i was told and i will pass it on to those who want it. an efficient compressor should not draw over 50% of its LRA rating. when it does it should have a start device installed. now there are many different devices out there such a ptc thermistors, "start boost" and a start capacitor with seprate potential relay both sized propely for the size and starting characteristics of the compressor. ie sized for the proper back emf of the compressor. also with my experience it is best to have a 10 amp feild installed fuse in series with the start capacitor. so when the relay or capacitor goes bad you blow a fuse instead of blowing up leaving that sweet smell of quick cheap fix from another service co.
dont get me wrong in most cases the "start boosts" will do the job in most cases but wait and see the fire works when the relay sitcks and burns a buch of wires. a guy i work with loves them and ive already had to replace 3 warranty ones and lots of rewiring. all only lasted less then a month. and yes some of the units were approacing 10 years old and theres also a lot of other varibles to consider.
but my experince with multi capable parts is that instead of being great at one application they are ok for most applications but not every application. if you would like more specifics on how to size a potental relay i will teach all who is willing to learn. just when i make over to the pro's. cya there sometime soon!