Seven month old 230V, 7.5hp, 1 phase motor with start/run capacitors having trouble starting natural gas well compressor. I am pretty sure the load is still the same. Once started the motor runs within specs. Could it be the start capacitor?
Yes the capacitor could be faulty or the centrifugal switch or a bad winding or connection. The switch being easy to test as it should be made with the motor stopped. The capacitor probably best to check by changing it. You can do a rough check on the windings with an ohm meter but this may not tell you if an internal fault is shorting some of the windings but if its not the switch or capacitor then the thing's probably junk anyway. You think the load is the same but this is a big motor for single phase and compressors are hard to start so you need to be sure. Single phase motors can be a ***** when they don't work so good luck.
Induction motors are about as simple as they get. Pretty much just a couple of coils of wire. If it runs okay and has trouble starting, it pretty much has to be the cap. That being said, some have a switch contact inside that closes when stopped to place the cap in circuit and opens when revs pick up taking the cap out of the circuit. Usually it will be a spring loaded contactor. If you have one, just inspect and clean as needed.
