First, I am assuming there is a "float" function on this machine and if so how do I use it. Also, what the heck is the "detent" in the valve? Mine is a late production model (2000 JAF0332---) if that helps. The rebuild continues as I work through the machine.
You engage float by pushing the loader lift control hard down. It should click in & hold the lever in place. However, the detents tend to get gummed up & stop it from working. Sometimes you can remove the end cap & free the detent balls & springs by cleaning them & fresh grease. If they are badly out of shape a repair kit should be available from CNH - with new cap / rod / & springs & balls. The pic below is from an 1840 but the same type of set up is used on the 1845C. As far as using it - I'm not an operator - you only would use it while grading backwards or while grabbing with a 4in1 bucket. Most operators tend to not use it - hence the reason why they stop working. It's handy when the engine is not running & you want to raise the loader frame using another machine.
Yes that looks just like the 1845C. Here is the parts page with part numbers. Note that there are two of the numbers 16, 22, and 19. When you put the hoist lever all the way down you should feel a snap when those balls #16 pop into the groove the arrow points to in item #17. You may be able to remove the screws #19 and spray penetrating oil in and free up the springs and balls then put some light grease in to lube them.
Larpy, I had the same issue and got help from members on this forum. The inside gets all gummy and the springs and small ball bearing do not engaged. I took it apart cleaned everything up. You can reach the Philip screww head for the cover from the back of the engine with a very long screwdriver.