As we park for longer periods at campgrounds I'd like to know if it's important to periodically start the engine to rebuild air pressure? After 5 days both tanks are currently showing 50 psi. If left would these tanks go to zero? Any harm?
IMO, no harm if the air tanks go to zero. Some coaches take longer than others to get to that point, which is good, cuz it indicates a "tight" air system. Even with zero pressure in the tanks, the air bags will hold pressure for a long time. When they do finally sag, the HWH aux air pump will add air to them, but only if it is required to maintain the auto-level.
Some members worry about having to drive off in a emergency situation when the air tanks are empty. Our old coach only has to idle for about 10 minutes to bring the air from zero to 100psi, at which time the air bags are fully inflated. I think that is quick enough to get the coach moved under almost any imaginable situation.
Starting and idling the engine just to maintain air pressure is not recommended. Some of us have permanently installed 120V air compressors in our coach, complete with filters and water separators, so we can "air up" to operating pressure without running the engine. Here are a couple threads - there are others:
Pancake compressor (split from How long to build air pressure?) (http://www.foreforums.com/index.php?topic=31691.0)
110V Aux Air Compressor Install (http://www.foreforums.com/index.php?topic=31836)
No need to keep the pressure up.
Just curious, since I don't have an on board compressor, will the air dryer function while filling from my shop air with engine off, and a valved tee upstream of the dryer. Or is there a heater element in the dryer that always on?
Heater is on with ignition, but you are going through the filter
The electric heater is just there to keep the purge valve from freezing in sub-zero conditions. Heater has nothing to do with the air drying function.
My air tanks go to zero within 24 hours or so. My airbags hold steady pressure for more than 3 months.
I do need to replace some air system components someday.
Looks like I am in luck, fitting going into air dryer is pipe thread, and there's room for a tee and a nipple. I started my coach last week sometime to get it raised up a bit to work on it, it's now down to 35 psi rear and 95 in the front, I can fit under it with the bags completely deflated with about 2" clear. But it's not easy. Adjustable 27" tall jackstands would be safer if a tire blew.
I would suggest having a air drier on the air compressor line, when using a outside compressor.
I don't get how that would be different, upstreame of the coach air dryer?