Originally Posted by lbrunning
The brakes sticking to the drums after a 2 or 3 week time period is not uncommon on semi trucks and trailers witch have the same basic air brake system as your coach. As far as the air dryer exhausting yes you can count on that to tell you that the system is full of air as the air governor sends a burst of air to unload the compressor at 130 to 135 psi and that is the same burst of air that purges the dryer
Yes, that "woosh" sound is the governor blowing off the excess pressure as you stated.
But an additional piece of info is that the compressor is clutchless and NEVER stops running (AFAIK, it is gear driven directly off the engine itself) and therefore is always operating (compressing), which is why you hear the governor blow off the excess pressure every so often.
As far as draining the tanks..... I pull my cables every few months whenever I happen to think of it. I have NEVER gotten more than a teaspoon or so of moisture out, even when I drove 18 wheelers.
Finally, the REALLY big problem would be during the winter, when that moisture could freeze and possibly render the entire brake system useless.