Product review (5 stars): From Hot Air to Cool Air
On really hot days, my 10-year old central A/C unit would not stay off very long before the thermostat called for it to turn on again. I would notice that the furnace blower would come on, but not be blowing cold air.  My electronic thermostat has a built-in 5 minute delay before it will call for cooling after the previous cycle has ended.  But this was not long enough for the pressures to equalize in the system, and the compressor could not start against the back pressure.

Installed this kit on the outdoor unit and problem solved.  it increases the starting torque enough to overcome the system back pressure.  Now I have cool air every time!