Product review (5 stars): Saved the life of an otherwise "dead" central AC system/compressor.
This literally saved the life of a central AC system (3 Ton 220V).  Two contractors before me came to look at it, and gave the same diagnosis (bad compressor, entire system needs to be replaced $6000).  I looked at this system as a favor to the homeowner, since someone else was messing with it, the first thing I did was recover the refrigerent, evacuate, and recharge to factory spec, then I saw The problem was the compressor would not start, every time the system called for cooling, it would hum for 2seconds and kick off on thermal overload protector.  I installed this about 3 months ago, and the compressor started right up, and unit began cooling immediately.  Unit has been running all season every day with no issues since installation.  If you have a compressor that is not starting (thermal overload shutdown), its definitely worth a $20 gamble to try one of these.  If you have a system that is simply "not getting cold", you need to do a little more troubleshooting before messing with one of these.  Update 6-14-2015 - unit is still running good as new a year later!  If you have a compressor that is not starting because it is cutting out on thermal overload (5 second hum then click), this is worth the gamble to try and save it.