Compressor won't turn off - PCM?

This year is our first using pneumatics, and we are encountering an odd problem. When we first set everything up to test, the compressor turned on and off just as it was supposed to, but now that everything has been transferred onto our robot it doesn’t. The compressor and pressure switch are both plugged in properly and there is a solenoid opened in the code, but the compressor won’t turn off once it reaches the maximum pressure. It actually turns on even when the pressure switch isn’t plugged into the PCM. I have already tried updating the firmware on the PCM to both 1.62 and 1.65. If anyone can help us figure out the problem, you’d be amazing!

Have you checked your pressure relief valve (the one with the hole/holes) to see if it is letting air out before the pressure switch can trigger? If not, that might be one reason. But that is really weird if the pressure switch is disconnected and it still runs. If it isn’t the relief valve, I would guess that you might have a faulty PCM.

Try a new PCM. If there is no switch, then the it should not turn on.

I’ll echo this. Also, contact CTRE about it - this is a bad/dangerous failure mode for the PCM, and they may want to investigate why it’s acting this way.

Check the power wires to the compressor and pressure sensor where they connect to the pcm, we had a similar issue caused by exposed wire contacting at the pcm

I agree - check for swarf (metal shavings) or another source of a short across the pressure switch terminals. If you can’t find anything, replace the PCM, preferably working with the vendor or CTRE.

Another thing to check: make sure the pressure switch isn’t shorted out; with the compressor running, unplug the switch. If the compressor keeps running, it’s a PCM issue (or swarf intrusion as some have mentioned). If not, the switch or its wiring is shorting out.

We have unplugged and replugged everything in three times, checking for shorts every time. We didn’t find any metal shavings, and even took the PCM apart trying to find any. Even if we unplug the pressure switch while the compressor is running, the compressor stays on. We are ordering a new PCM to test tonight. Until then, we have the pressure switch plugged in as a digital input and are controlling the compressor through code in teleop while we test.

Don’t forget that for competition you need to either switch back to a PCM or put the compressor on a spike (R88 C and D).

Yeah, I’d RMA that PCM. That’s clearly a PCM issue.