starting capacitor staying engaged

I have a arco hd25 hp RPC when i power the unit up, it comes up full speed within about 5 sec, but it making a humming noise. there is an electric contactor that stays engaged when the rpc is up an running, which i think it is suppose to cut off, when up to full speed. I thought it was the relay, so i replaced it, not the same brand but the same diagram on the side. The problem still exist, the relay is hooked up the same way the other one was 1, 2 and5. but not 100% sure if correct.
Inside the panel of rpc is 2 starting caps, a series of run caps, relay and contactor.
I thought sure it was the relay but now im left scratching my head. Voltage on 3rd leg is 276 which i thought was high. Any help will be appreciated

Most motors have available replacement parts for the centrifugal switch, which mounts to the shaft inside the motor housing. If it wasn't the relay, you'll probably have to go inside the motor itself and see if the switch is stuck.

OK thanks I was thinking the relay sinced the voltage change and and turned off the starting caps. It was working fine till I moved it closer to my service entrance.

My smaller Arco has no start caps, just one start/run. But I don't think any of them have start switches.

If you have a relay, it should be to cut off the start caps when the thing is generating a high enough voltage, just as you think.

Do you have an internal wiring diagram?

I do not have any data on this unit bought it used. I may can contact the manufacture and get one.