Installed icemaker to existing water line that had not been used for several years. debris was forced into water line on frig.. can you suggest how to flush water line to remove debris?

Trace water supply line to where it connects to back of unit and locate the solenoid valve. This is a small electric valve that controls water supply to ice maker. They are usually connected with compression fittings so slightly loosen compression nut on inlet side to see if you have water to that point. If no water there then backtrack water line to source and make sure water line is hooked up and valve is on.
If you have water to inlet side of solenoid valve manually actuate ice maker and listen to hear if valve is opening. IF not then valve will need replaced. If you have water to valve and valve is opening then shut off water supply valve. Renove compression nut and clean inlet screen and put back together. Check to make sure filter is open . Remove line from outlet of solenoid and blow thru it to make sure its open into freezer. Hope this helps you. Thanks

The bleach idea sounds the best. How did you get the bleach into the system? It would have to be under pressure from the water inlet to the connection on the refrig, running the water dispenser for several minutes until you could smell the bleach from the dispensed water, plus the icemaker would need to be cycled, and then left for at least 15 minutes to an hour, then flushed with clear water. (again, several, as in about 10, minutes for this step) (icemaker line also needs to be flushed with clear water) Best to be done with the filter bypass plug in place, then when done, a new filter. It is not really possible to replace all the water lines, as the one inside the freezer door cannot be replaced without replacing the entire door.

Yes, it was hooked up at the last location, but I wasn't the one who put installed the frig, and the movers disconnected it, so I don't know how it was done.

Remove the food from the freezer , then remove the icemaker , if it has one ( 2 screws ) . Remove the rear freezer panel . Useing a hair dryer , start in the middle of the drain trough , and defrost until you see the drain hole . Keep defrosting the hole ( hot water helps ) until water will go thru . Use a piece of tubing inserted into the hole , and blow thru , to remove any debris accumulated in drain line .Remove any excess ice from trough . Reassemble freezer .

Check the water valve at the back of the fridge if present.

Even if you used blowdryer, ensure that linse are not frozen by performing a complete defrost.

Disconnect water lines from icemaker, and blow with compressor if the above did not work.

IM USE A 1/4 INCH WATER LINE LOOK FOR A SINK OR WASHER CLOUSE BY AND ATACH TO THE HOT WATER LIND IF YOU HAVE LIME IN YOUR STATE IF NOT USE THE COLD WATER RUNTHE HOSE INSIDE THE CAVINET TO HIDE THE HOSE.

•  if the cubes that the icemaker makes are full size then... the water valve on the back of the machine is usually the culprit in these cases. it will not close fast enough resulting in a little overflow of water into the auger assembly every time it makes ice. it only takes a little bit of water to settle in the bottom of the pan to cause problems. 
  
• if the cubes are smaller than what you would expect then the water is leaking out right before it reaches the icemaker. either from the plastic tube behind the icemaker or the cup on the icemaker that funnels the water into the icemaker.
• it also could be the timer inside the icemaker leaving the water valve on too long.
• all these things can be tested on site. the service person must not be very well trained.

if you already checked this and think it is a different problem then let me know, i will help you figure it out. 
Mike  

you most likely have a short in the ice maker ..the ice should be ejected before the water is call for... you need a new ice make or if you can change the ice maker head let me know and I can help

Its a done deal...:) On MY whirlpool MODEL # ETICHMXKBO3 I found the drain hole frozen.. There was some debris and clogged it up and water froze up behind it causing the deck of my freezer to fill and freeze up and cause the water to drain into the fridge. Solution: remove the ice maker(if equipped) remove the rear aluminum cover. I used a heat gun and melted the 1 1/2 of ice build up and softly with a screw driver clean the drain. When drain is visible use scolding hot water until it starts flowing to the bottom tray. I used my air compressor to finish it off....

excessive water pressure to the house?
deffective tubing ?
is he using the plastic ferrel and brass insert
if not you must