05 Columbia loosing air pressure

Mine did that one time, but it quit after I rebuilt the purge valve etc.
It would keep blowing off until I tapped it, worse in cold weather IIRC.
Did you completely drain the tanks?
If not, then do that too.
I am starting to think you maybe have a bad part number for the purge valve, as that is the only thing that is blowing air out by the sounds of it.
When you put the new purge valve in there, did it slide in nice and easy, or was it a SOB to get in there? Maybe a scored bore in the air dryer, where the purge valve slides in? I had to use some wet and dry sandpaper on mine to get it to slide nicely, then applied molylube to keep it free. Never had it apart again in @3yrs after that.

Martin

 

Check you blue line to your trailer if you have a big leak avery time you step on the break air will come out but only when you step on the breaks.

 

If you've got an SKF Turbo 2000 dryer I've noticed they have a habit of gumming up around the purge port and sticking.

Excessive water in the tanks would cause your air pressure to drop faster on brake applications and build up faster since the water is not compressible and takes up tank volume.

Did you check the discharge line off the compressor for carbon buildup?

@GrapeApe is pretty knowledgeable with this sort of stuff. Maybe he'll chime in.

 

Thread is a few years old. A lot of really old threads getting dug up since the new software, I even did it once myself. I think what's happening is this the new boards have a sort function if you click on the columns at the top of each forum. If you accidentally click on one it sorts the threads by that header which can put old threads at the top.

 

Holy crap I didn't even notice that. I hope buddy got his air problem sorted out by now.