York Stellar furnace model M3UF032SA. About 18 years old
I am investigating the blue box that sits on the floor next to my York Furnace. I hear it cycle on and off, but I must admit I'm clueless about what it does. Water seems to have collected under the box, so I'm wondering what sort of maintenance I need to perform on it.
Any help would be most appreciated.

Is it a pump? Does it have a tube that goes to a drain?

This is a condensate pump. It is to get rid of the water that collects on the coils of your AC and runs into the box which is just a collection box for the water. There is a float in the box that turns the pump on as the water reaches a certain level, it pumps down to a level where the pump cuts off.

There also maybe a float in the same box that will turn the AC off if the pump fails to pump the water out of the box. As to why there is water under the box you will just have to inspect around to see why the water is there, I don't think it would be a crack in the plastic box but it could be the box is getting too full of water.

Thanks for your help. I think the water was actually coming from the hot water heater next to it. That should be fun!

New water heater time.

I have a York Stellar heat pump... Recently switched to A/C... A/C seems to work for a short period than no cooling... ice accumulates where copper lines leave outside unit. Worked fine last summer. Heat was fine all winter. HELP