Icemaker not making ice. Water supply is good, turned on icemaker; solenoid resistance is 338 Ohms. Can't blow through plastic water supply tube at back of refrigerator. Supply valve screen had some coppersulphate on supply side, but certainly not enough to block - maybe blockage inside box? Plastic supply tube is clear. What to do?

An icemaker receives water through a small, 1/4-inch water supply line that runs from the refrigerator to a water pipe, where it is connected by a tap valve. The water supply line enters a valve in the refrigerator that is controlled by an electric solenoid that sends water through a fill tube into a mechanized icemaker assembly. There, the water freezes and is dumped into an ice bin. When the bin is full, the ice lifts a bail wire that turns off the icemaker. If the water’s route is blocked or the solenoid doesn’t work—or if the bail wire is lifted—the icemaker won’t make ice. (Also note that your home’s water pressure must be strong enough to serve an icemaker.)
Here are a few steps you can take to get your icemaker working (be sure the bail wire above the ice tray is in the down position):
1) If the icemaker doesn’t make ice but you can see the arm swing into motion and you hear a buzz for about 10 seconds after it is finished, the water valve is asking for water that isn’t arriving. This means the valve and the solenoid are probably okay, but the water supply is not. Be sure the water supply line isn’t kinked behind or beneath the refrigerator (1/4-inch copper tubing is much better than plastic fill line).
2) Check to see if something has caused ice to back up around the mechanism—this can cause the fill tube to freeze, blocking the mechanism. When ice cubes are small and seem to be getting smaller, it generally indicates a frozen fill tube.
3) Check the water line that enters the back of the freezer for a blockage. Find the water shut-off valve behind the refrigerator or under the sink, turn it off, unscrew the copper line from the back of the refrigerator, put the copper line in a bucket, turn on the valve, and see if pressurized water pours out.
4) Check the tap valve; a bad tap valve may cause the problem where the icemaker’s supply tube connects to the water pipe. If necessary, replace the inlet valve and the tap valve. For the tap valve, use the type that requires you to drill a 1/4-inch hole (as opposed to the “self-piercing” type). You can do this yourself, or call a repairperson or plumber to install an inline water filter when replacing the valve.
5) The water line attaches to a solenoid at the back of the refrigerator and then travels to the icemaker. The solenoid may be defective or may not be receiving power. You can try removing the sediment screen inside the solenoid and flushing it with water to clean it, and at the same time you can inspect any seals or diaphragms to ensure that they are sound. Unplug the refrigerator first. Unless you’re skilled at home repairs, this job is better left in the hands of an appliance repairperson.