any truck mechanics around?

i have a problem i cant solve, its on a 2004 330 peterbilt, the air dryer has gone nuts, it doesn't cycle any more often than it usually does, but when it does cycle it stays on, for an extended period of time, as much as 5 minutes, we replaced the dissant filter in it, but that didn't change anything, we haven't had any moisture in at least 6 months so it isn't wet air, any other ideas?

Have you taken the valve on the bottom apart and cleaned it? Sounds like you have something in there or the spring came off its seat.

When you say cycle do you mean it purges air for 5 min's? if so I'd start by changing the purge valve could be sticking

we did clean that valve but ill recheck it

You did not say what kind of air dryer. But one thing to check is the air compressor governor or unloading valve. They will cause this problem. Also did you rebuild the air dyer head when you replaced the cartridge.

I just change the whole thing with a new one. I had friends that had the one with the spin on cartridge. They were always froze up in the winter.
When I ordered my new Pete back in 2000 I had them put the old AD-9 on it got changed for the first time about a year ago.
The guy that does my inspections said the corrosion on the aluminum doesn't pay to replace parts in them. The valves won't seal.

Rebuild the purge valve. My 2 cents

thanks guys i didn't rebuild the dryer as the thing looked to be in pretty good shape this tuck stays in the southwest, and doesn't run in snow much , it may well be the governor,the truck is bumping on 300,000 miles, i hadn't thought of that mind block i guess when it comes on it does bleed air continuously, it will finally cut off but it runs way too long at a time

By 'staying on' I assume you mean that the purge vave in the bottom continues to purge? If that's the case... replace the purge valve. If that's a Bendix AD9 dryer it's not a big deal. Just make sure you know what you got before you go looking for parts.

Rod

i met a guy on a run with my grandfather and his air drier was stopped up my grandfather told him to tie the line together he looked at him like he was full of it but did it anyway and it built up air and he was back on the road again

I've got to agree with the others here, check the purge valve and the governor. I had a similar problem with the dryer on my Freightliner. It was about time to replace the dessicant cartridge so I did that and rebuilt the purge valve at the same time. The problem of the valve staying open for an extended period got a bit better but never went away. I then started to notice that if I tapped the brakes a few times and made the air pressure drop enough for the governor to allow the compressor to start building air again it would stop. In my case I had also started having issues with the brakes seeming weak when applied. The guage on the dash read equally for both the primary and secondary sides of the system, and the low air buzzer came on around 70 psi, but the brakes still felt weak. When I installed a different guage in the system I found I was only running around 105 psi system pressure, so I jacked it on up to between 125 and 130 where it should have been all along. Now it reads nearly 150 on the dash guage, the low air still goes off around 70, and the purge valve does it's thing without staying open too long like it had been doing.

That said I know on mine the purge valve senses system pressure and cycles based on what the governor is doing. I can't say exactly how it goes about the cycle but, based on my experience, it's cycle time open must have something to do with a pressure differential in the system. In my case, with system pressure too low (at a certain pressure point anyways), it stayed open way to long and would not shut on it's own. However if I made the pressure drop a bit more so the governor kicked in it would close almost immediately when the compressor started pumping and system pressure started to rise.

I know this whole deal about drove me crazy trying to figure out since I was trusting the air guages on the dash to begin with. Once I used a third, known, guage to look at things with a different eye, everything fell into place and I haven't had any more problems out of my braking system as far as the purge valve goes, and the stopping power is now better than it's been since I bought the truck since it's actually running a proper pressure now vs being nearly 20 psi low.

To try to explain how it works a bit... The purge valve is sent a pressure signal from the governor when the compressor cuts out. If you think about a shop air compressor, the air release when the compressor unloads as it stops is the same thing that opens the purge valve on your truck. The purge valve could be sticking, it could be the governor, or, not likely, but it could be an internal leak in the compressor. Pay attention to when the purge valve closes, if its when the compressor starts pumping again, I would change the governor and go from there. Governors are cheap anyways.