How do you check the compressor ,start capacitor for a residential a/c unit,if it has three legs ,terminals?

Question

after capacitor is discharged first of course.

Answer 1

I am not sure what type of a/c  that you are referring to,but most don't have a capacitor like you mention. If it has three legs.one is for a ground,and the other two are for the power required to operate the unit. If you are talking about a relay,they control voltage,not store it. If the applied voltage does not cause the compressor to turn,three things could be wrong. One,it is broken,or two,it is low on freon.or three,the relay is not telling it to come on.

Answer 2

the compressor has three pins common start and run, inside the comp is a overload if the comp is real hot the overload will be open. you take a OHM meter and read from c to r and c to s most comp will have under 1 ohm resistance. Check each pin to ground if you get a reading the comp is bad. The capacitor checks with ohm meter and the needle should jump and fall back down, if it stays steady the cap is shorted. look at the cap if it is rounded on the top or bottom it is bad, it is common for caps to swell up and go bad.

Answer 3

If the run capacitor is bad, it will be bulged or leaking oil.