Hello,
I'm having a issue with the PCS switch and the independent brake. From full application on the independent it will release until you get to about 25 psi. Then you hear air exhaust which sounds like from under the cab floor and then the PCS opens. Train brake is ok. PCS resets. Cylinder pressure set at 72 psi. Former NS GP38-2

Thank You

I've seen that a couple times. Sounds like air bleeding from the independent side to the automatic side on application, assuming you're not MUed with another unit. When you release, the partially charged automatic is holding air and dumping it as soon as the independent control drops low enough. Was a long time ago so I'm not sure what the fix was, but probably a bad diaphragm in either the brake cylinder relay valve or an A-1/A-2 reduction selector if your unit is equipped.

I have a couple of questions first, when you release the independent brake and PCS opens up, do you get a penalty brake application? In other words, does the brake pipe pressure automatically reduce by about 26 psi and then stop? Also, is this locomotive equipped with an alerter? In the way in which you described this problem, what it sounds like to me is that the P2A application valve is being allowed to induce a penalty brake application once you deplete air out of the 26 pipe (i.e. release the independent brake). This could be because air is exhausting out of the 3 pipe due to the alerter magnet valve (or some other device) is not staying picked up or possibly because the P2A valve itself is in fact defective. I would start by checking that the alerter magnet valve is not dropping out and causing the 3 pipe to exhaust.

Hopefully this will give you some ideas and point you in the right direction.

If you have a event recorder failure which would the brakes not work as intended. Also it can be pcs pressure switch is leaking disconnected or plug it up. also your exhaust leak could be magnet valve has no power going to it . if you need more help send me private message

Is this an operational unit that recently developed this problem, or is this an old unit being restored off the dead line that hasn't run in 30 years?

I presume this ex-NS GP38 still has its alerter? If it does, try this: Hold the alerter reset while you release the independent brake. I've had one that would do what you're describing when I worked for NS. The fix was that, hold the reset button down when releasing the ind. brake. I'm not saying that is how it SHOULD work, but that was how one I caught once was behaving.

I was looking at our unit a couple of months ago and noticed there was a line coming from a 3 way check valve and the P2A that was capped off for some reason, I didn't have a 26L book around so I connected it back to where it was supposed to go that was an open like right next to it, I fired the unit back up and this exact problem happened, I have not had a chance to dig into this more but was there ever a solution to the above problem?

I was thinking ours was the P2A but was never able to swap it out yet.