Compressor doesn't shut off properly

[oldman_pottering]

My compressor recently started to have trouble shutting off after it built up pressure, instead of shutting off cleanly it would cycle on and off like it didn't know what it wanted. I pulled the pressure switch apart and found that the contacts were looking pretty ordinary so i cleaned them up and everything was good for a little while then the trouble started again. This time I replaced the switch and all was good for a few months, I should note that the on off switch never worked after replacing the pressure switch, but I only ever turn it off at the wall ( compressor normally gets used every weekend ) , yesterday it started playing up again so I took off the pressure switch cover off and ran the compressor and noted a fairly bright flash from the contacts when it reached cutout pressure and it did cutout as it should but I can definitely hear the motor change pitch as it reaches maximum pressure. This motor had been replaced years ago by a electrical repairer in town but he doesn't do these repairs any more.
is it possible the motor is starting to draw too much current as it nears cutoff pressure overloading the pressure switch contacts ?
Any help or advise on testing etc is appreciated

 

[PCustoms]

Post a pic of the switch, showing the wiring and the contacts if possible.

How did you "clean them up"?

What are your pressure settings at the switch and the tank reading?

240v or 120v?

 

[oldman_pottering]

Post a pic of the switch, showing the wiring and the contacts if possible.

How did you "clean them up"?

What are your pressure settings at the switch and the tank reading?

240v or 120v?

Hi mate, thanks for the quick reply
I cleaned up the contacts initially with fine wet and dry paper and sprayed them with contact cleaner
I'm in Australia so its all 240v ( I forget when posting on international forums about other voltages)
I will check the pressure settings and get a photo tonight. I'm at work at the moment, it's 8.30am here and so my response will be delayed
thanks again

 

[PCustoms]

Hi mate, thanks for the quick reply
I cleaned up the contacts initially with fine wet and dry paper and sprayed them with contact cleaner

Hate to break it to you, but those contacts are shot now.

As part of the troubleshooting you'll want to get a new switch installed first. Once the plating is damaged the contacts can arc/stick and not release correctly.

Could have been your initial issue, sanding is a temp fix until the next arc.

 

[oldman_pottering]

Hate to break it to you, but those contacts are shot now.

As part of the troubleshooting you'll want to get a new switch installed first. Once the plating is damaged the contacts can arc/stick and not release correctly.

Could have been your initial issue, sanding is a temp fix until the next arc.

Correct, I may not have paragraphed my first post that well but after the cleaning of contacts didn't work I replaced the switch but now a short time after the new switch is giving the same trouble

 

[The Cobbler]

are these switches rated for the current the motor is drawing, or is it possible you're exceeding the ratings of the switches?

 

[PCustoms]

Correct, I may not have paragraphed my first post that well but after the cleaning of contacts didn't work I replaced the switch but now a short time after the new switch is giving the same trouble

Woops,I missed that. Disregard my comments about the arcing (for now).

Let's go back to the basics:

are these switches rated for the current the motor is drawing, or is it possible you're exceeding the ratings of the switches?

Checking this and posting some pics later will go a long ways to getting this solved

 

[john.k]

The pressure switches dont last...unless you have a contactor as well to handle the current draw .........my old Servex has a mercury switch that tilts a glass vial as the pressure builds .........this is completely reliable,.......but it works a contactor that sticks and had to be hit with a spanner to switch off or the safety valve starts to blow.

 

[nadogail]

Electrical problems don't announce themselves with a Bolt of Lightning or or Clap of Thunder, sometimes you have to apply real thought and effort to find them.

 

[oldman_pottering]

are these switches rated for the current the motor is drawing, or is it possible you're exceeding the ratings of the switches?

will check for more info tonight

 

[oldman_pottering]

Electrical problems don't announce themselves with a Bolt of Lightning or or Clap of Thunder, sometimes you have to apply real thought and effort to find them.

exactly ! I'm hoping to get this sorted before that happens

 

[oldman_pottering]

Update:
when I replaced the pressure switch I fitted it as is, I didn't make any changes to the spring tensions
the tag on the switch ( hidden by wiring) lists the pressures in KPA but equivalent to 95psi - 125 psi
the compressor has been cutting out at 100psi

 

[oldman_pottering]

Update :
I was considering rewiring to bypass the pressure switch as a test but then thought I might as well pop the electrical cover off, lo and behold here is the run capacitor swollen and blown out, replaced that with one bought off Ebay and its good to go now. Don't know why I guessed it was a switch fault without checking anything out, lesson learnt and I'm back in business