Singer 4423 feed dogs are not working properly. Tested and verified that this happens without any thread in the machine. The dogs are not lowered. We've cleaned it and still no luck.

I just had this same problem and I fixed it by removing the bottom cover under the free arm. There is a plastic wheel on the rod that spins when you sew that plastic wheel needs to be all the way to the left to raise the feed dogs. I think the lever is supposed to move it back and forth but my guess is the lever can slip past it and not be in the correct position to move it back. Good luck to all happy sewing

Now, I'm assuming that you pushed the feed dog lever in the back to the left successfully. If you couldn't make it move, try pushing the lever down and then to the left. You don't see any difference when that happens, because the feed dogs are actually ALWAYS down -- during ordinary sewing, they rise up to grab and push the fabric, then go down again. Turn the hand wheel (ALWAYS towards you) while looking at the feed dogs and see if they rise up during the cycle. I'll bet you DID lower them, but didn't realize it. What is actually does when you lower them is disengage the mechanism that makes them go up and down.

One more thing -- to set them in the up position again, you have to set the lever, then turn the hand wheel several times -- sometimes as much as five cycles -- and then you'll hear a click. That is true of ALL sewing/embroidery machines.