We think the controls are leaking air but in the meantime is there anyway to do it manually?
Most dump truck hoists are a mechanical linkage as far as I know. Air shouldn't cause it to not come down. Maybe very carefully check the linkage to make sure the spool on the valve is moving enough to allow oil to return. Maybe you can work the valve right at the spool? As a very last resort you could loosen the hose(s) to the hoist cylinder(s) and the weight of the box should come down and push the oil out. Have a big pail ready to catch the oil and only loosen the fitting slightly. Better to have it lower as slow as possible than to come crashing down. Be very careful so you don't get crushed.
You probably already got it down, but depending on your set up, there should be an air piston on the side of the pump, Sometimes they get dirt in them, or maybe it is leaking by, but you should be able to move it by hand if the air is unhooked.
We got it down.
How, what was the problem why it wouldn't go down?
The air wasn't pushing a switch/valve so we had to do it manually. Just a simple push and it came right down.