I currently have a 5/16 pex line running from my reverse osmosis filter under my sink to my refrigerator under the floor through the basement and up to a little opening in the wall behind the refrigerator. This has worked nicely for the past year that I've owned the house, but now I'm getting a new fridge and plan to install an ice maker outlet box in the wall. It has a 1/2 inch push connector, so my question is if it will be fine to couple the 5/16 line to a 5/16-1/4 reducer and then connect the 1/4 to a 1/4-1/2 reducer that will push into the ice maker outlet box. It's not very practical for me to try to run a new line for a variety of reason, so I want to leave that 5/16 in place if possible.
Adapting the size will work fine as long as there is enough flow to fill. some units are on timers and if the flow is low this reduces the quantity of ice made with each batch. I have found fridges connected with saddle valves and a tiny orifice of only 1/16" was sufficient until the tiny orifice in the piercing screw got plugged. I don't like saddle valves because in my experiance they always leak. I usually add a double outlet valve or a t and a shutoff where I tap the water line in case the line to the fridge gets kinked. My wife is OCD with cleaning and the fridge regularly gets pulled out for cleaning and has pulled the line loose in the past so a shutoff at the point of connection is mandatory at my house and a good idea every place else.