I grew up in a slaughter plant where we slaughtered everything from chickens to cattle. The scalding temperature is critical to your success. It really should not vary more than a few degrees from 148F. Pigs were the same and I have done thousands of them. If you scald too hot the skin gets very gummy and feathers stick like glue. Too cold is almost better, but below 140 and sometimes the feathers wont loosen.
Dunk the chicken up and down in 148 degree water, When the feathers on the thigh slip very easily dip for just a few more seconds and get them out of the water. Use a good rubbing motion with your hand to rub the feathers out, the wing and tail feathers need to be literally pulled. After you have most of the feathers off use some water to clean the sticky feathers then a knife or something for pin feathers.
It is a mess under the best of circumstances but make certain you dont get them to hot it makes a real mess