Short version: not needed, overprice, uniformed/misguided/dishonest, 1 more thing to break, cheap electrical parts like to melt and potentially start fire.
A hard start kit creates a lot of additional starting torque. It’s a $15 part. There’s a half dozen conditions why one would be needed (some listed at bottom). But if you’ve never had any problems starting you don’t have any of them and it’s not worth $15 let alone 200.
Additional torque will get the compressor from 0 to 3450 RPM’s faster. So you will use less electricity…for less than 1 second at start-up. So yes you will use less electricity. But so little less you would never be able to measure it in any practical or reasonable way.
As far as premature failure (whatever “premature” means) additional starting torque is good, but not really beneficial if you don’t have the reasons listed.
The hard start kit is a great tool to try to break free a seized motor and get it running again. So if your motor was to seize up (locked rotor) and that extra torque then broke it free on the next start, or after it cooled off (Some huge ifs). Well it didn’t really prevent anything, it just sort of repaired it and you never knew. So that’s sort of true…should the motor have that one specific type of failure but not so to bad that the additional torque could overcome it.
Now if a technician ever tells you a single phase compressor (or even a fan motor in some cases) is locked rotor, ask them if they have a hard start kit on their truck and ask them if they tried it. It might save you a lot of money.
Would I add one to any and every unit, no way.
Needed when:
Low voltage, like below 198V.
No 5 minute time delay built into thermostat or outdoor unit to allow pressures to equalize between cycles.
Metering devise that does not allow for equalization during off cycle.
Really long refrigerant pipes, like 150+’.
