My air dryer has started to unload with the engine not running.
Why R dat ! ? It does it after a couple of days, when the pressure gage is indicating low pressures.
It has did it twice that I have heard. Only started recently as far as I can ascertain!
Bill,
Mine gave me a few hints that all was not well but I didn't get the message until I was sitting on the side of the road without airpressure.
If your dryer hasn't been serviced in the last 5 or 7 years it's time to look into an exchange unit or a kit you can install.
I think it's sending you a message
I service and rebuild mine every 3 years, you can usually find the parts on line, or about any truck parts store, just get the tag # (model #) off the old one.
They can be done in place, however much easier out of the vehicle. The first time you do it most of the fittings are way tight, no need to over tighten them when you put it back.