"I’m running a 2022 Pete and I’ve noticed that even though my air dryer purges every few minutes, I’m still getting a mist of water when I pull my drain cords during my post-trip. I thought these newer AD-IS systems were supposed to handle the moisture for me. Is this normal with the humidity lately, or is my air dryer failing? I don’t want to deal with frozen brake valves once I head north into the snow next week."
Mechanic Answer:
"The air dryer is your first line of defense, but it isn’t a 'set it and forget it' part. If you’re seeing water in your tanks, your system is already compromised."
On a heavy-duty rig, your compressor is constantly fighting heat and humidity. When that hot air hits the wet tank, condensation is inevitable. If that water stays there, it’s a direct threat to your ABS modulators and your safety.
The Daily Pull: You need to pull your drain cords on the supply, primary, and secondary tanks every single day. If you get a clean "hiss" of air, your dryer is doing its job. If you get a mist or a spray, your desiccant is saturated and needs to be swapped.
Winter Prep: Water in your lines is the #1 cause of frozen brakes. One frozen relay valve in the middle of a mountain pass can ruin your week. If you haven't changed your dryer cartridge in the last 12 months, do it before the first freeze.
The 'Milkshake' Test: Look at the color of what comes out of those tanks. Clear water means a bad dryer. Milky or oily sludge means your compressor is "passing oil." If you see oil, a new dryer won't fix it—you’ve got a tired compressor gunking up your valves.
Pro Tip: Don't just rely on the automatic purge. Manual draining is your best early warning system. If you're tired of crawling under the rail, spend the $40 on a set of stainless steel pull cables so you can check them properly during your walk-around.