re: been meaning to order a spare A/C capacitor all summer

if you know or can find you unit's model number you can likely look it up on the internet, but it's easy to just remove the cover on the unit and see what is currently in it

you are looking for the capacitance value on your capacitor's label...it's a number followed by either MFD or uF (for microfarads)...some have 2 capacitors internally, one is the capacitor for the compressor and the other is the capacitor for the fan, so they'll list 2 numbers...mine was a 40/5 MFD meaning it has a 40 MFD and 5 MFD capacitor bundled together internally and so has 3 terminals

you also want to match the max rated AC voltage that yours lists...in the picture below this one was rated for 370 or 440 VAC...as long as the replacement meets or exceeds this max VAC you are good