https://www.dallashvacparts.com/
The power surge during the storm yesterday blew out one of my ACs dual run capacitors. Went to Dallas HVAC Parts and picked up a new one. Great guys, very friendly. They are open until 1pm on Sundays. Kept us from roasting today and not having to call an HVAC company to replace a $32 part for $300.
Tanners has capacitors too. They are open til 3 on Saturdays. Capacitors are probably the most common issue. If you replace an old one with a new one, your chances are great that you will be replacing it within a couple years.
Ditto.
For me, it was also Memorial Day weekend, Sunday. Still open. Still had what I needed.
@TBJK, I seem to replace them every 2 to 3 years. @zmetzing, I did exactly that and bought 2 extra for the next time.
I was told to get a Supco Hard Start kit and it would help with caps lasting longer. Don’t know much about them other than they are easy to install.
One other interesting thing I learned about ACs after the power surge. Both ACs compressors were out. I thought it might have taken out both caps. So I tested the MFD’s and found out that one was indeed bad, but the larger unit was still good. Turned out that the internal circuit breaker of the compressor had tripped and needed resetting. I have never seen that before. But here is what I did:
1.) Set the thermostat to the 0FF position
2.) switched the AC breaker OFF at the panel.
3.) then switched the AC breaker ON at the panel
4.) let it sit for 30 Minutes
5.) them turned the thermostat to cool.
That did it, the compressor for that unit came back on.
The compressor has internal thermal overloads. Another common trick is to throw a bag of ice on top of the compressor until they reset. I would advise against a hardstart kit. Usually it’s a last ditch effort to limp the unit along.
Why is that? And roughly how long should they last?
EDIT:
I get that if the cap has failed you can measure that, but is there a way to determine that it’s on its way to failure?
It depends on the quality. My neighbor replaced his unit about 5 years ago. He has replaced his capacitors no less than 3 times.
Now that may be because the factory mis-sized them from the get go or the capacitors are just made like crap.
My unit has the original capacitors (92).
You can test it with a meter to see if it’s within spec but it is a crap shot to catch it in time.
I’ve owned some expensive ones and none of them had that function. 
I bought the Anatek Corp ESR meter years ago and love it.
Chris: There are a couple of ESR meters in Electronics, but that would require you to pull the cap and bring it in.
Tim, the caps these days seem to be crap. Keep your 92 and hope it last many more years.