Compressor doesn't start in its own

[bmwpower]

Since the winter, I've noticed my Quincy doesn't start on its own who the pressure gets low to trigger a start. I've fiddled around with the pressure switch and sometimes it will start. No separate motor starter. It's a 3hp motor.

Any suggestions on the issue? I assume it's either the pressure switch, the capacitors or the motor in general, but how do I determine which one it is?

 

[The Cobbler]

when you say it doesn't start on its own, does it hum and if you spin the motor it starts? then its start cap or switch. if there's simply no power to the motor it's likely the switch.
test the pressure switch (with the power off ) with pressure low in tank ( when it should kick on) . could be one of the contacts not making contact.

 

[zkling]

What pump setup are you running? Does it have hydraulic unloaders? Mostly likely the pressure switch is sticking if it runs fine otherwise. As The Cobbler mentioned, try to get it to not start, yet low enough to where it should run and put a volt meter on the output of the pressure switch / motor input. That will show if you are getting voltage out of the switch.

 

[bmwpower]

when you say it doesn't start on its own, does it hum and if you spin the motor it starts? then its start cap or switch. if there's simply no power to the motor it's likely the switch.
test the pressure switch (with the power off ) with pressure low in tank ( when it should kick on) . could be one of the contacts not making contact.

No humming. Just doesn't kick on. How do you safely spin the motor to see if it kicks on?

Sometimes I can get it to kick on when I press the manual switch on the side of the pressure switch a bunch of times, or adjust the pressure setting down/up and then return to the original setting, then press the manual switch a bunch of times.

 

[bmwpower]

What pump setup are you running? Does it have hydraulic unloaders? Mostly likely the pressure switch is sticking if it runs fine otherwise. As The Cobbler mentioned, try to get it to not start, yet low enough to where it should run and put a volt meter on the output of the pressure switch / motor input. That will show if you are getting voltage out of the switch.

Makes sense. I will give that a try in a bit.

 

[The Cobbler]

if the motor is not humming doubtful it's the start circuit ... sounds like your pressure switch crapped out. do you have a volt meter? check for voltage on the motor side of the switch or for continuity between the contacts ( with the power off)

if no volt meter you can rig up a light bulb on the motor side of the switch to see if it is lighting when the switch closes . again, sounds like your pressure switch