Air suspension bags not inflating

If there was a suspesion dump, there would be a switch for it on the dash. Not sure where else it would be. Do you airbags have holes in them? Did you check the lines you use to empty your air tanks? Make sure one of those aren't stuck open.

 

Had the same problem on a T2000, 2001. Turned out one bag had a cut in it.

In my mind I expected there to be a loud hissing - there wasn’t.

Soapy water all over them -

 

Sounds like the pressure protection valve is bad. It feeds the leveling valve off the air tank.

 

First visually check the linkage on the leveling valve to make sure it's connected and not bent/broken and listen for air leaks. Then make sure you have air pressure to the leveling valve. If not, check the pressure protection valve. If your valve has an internal dump function, it should be a normally closed valve, pull that air line and make sure that it has no pressure unless the dump switch is flipped. There valves with normally open dump valves for certain applications that I have seen put on by mistake, but this is obliviously a problem that starts as soon as you change the valve, not something that just starts having problems one day.

Some FLD's had external dump valves, usually on the rear cross-member (if they had them), they were known for sticking. You can bypass them to check them. External valves were more common in the 90's, so you may not have that.

If everything checks out so far, disconnect the linkage and the line(s) going to the bags and manually move the lever to see if you can get air through the valve.

 

Ice?

 

No. The warning light (I'm assuming it's the suspension dump light) is just a pressure switch in the line from the dump switch to the leveling valve (or external dump valves). Your dump switch might be bad and allowing air through to dump the bags, which would also trigger the suspension light swtich). Pull the dump line off the valve and see if it has air with the switch off.