Cut up the onion, celery and carrots and put them in the bottom of your crock pot. You are not going to eat these with the chicken, they stay there for making stock. Limp veggies are OK for this part. Putting them in the bottom of the crock pot keeps the chicken elevated out of the juice and lets the bird roast instead of stew.
Combine the garlic cloves, olive oil, salt, and pepper. Add about 1/2 tsp of the fresh thyme leaves or all of the dried thyme. I combine in a small food processor, but you can do this by hand.
Remove all the stuff they pack on the inside of your chicken and place them (neck and innards, NOT the plastic bag) in the crock pot with the veggies. You aren't eating innards, but they DO make the stock taste richer. Remove as much of the excess chicken fat as is practical.
Take the garlic paste and spread it under the skin of the chicken. Try not to poke holes in the skin. Make sure you flavor the breasts and thighs. Now stuff the orange or lemon slices and fresh thyme (if using) under the skin as well. If you have extra, place it in the middle of the bird.
Roast in your crock pot for 3 to 4 hours on hi.
Remove chicken and enjoy for dinner. Add 2 cups of water to your crock pot and turn it to LO.
I remove the thighs, legs and wings to a platter for serving. I put the breasts into a ziptop bag for use in another meal unless we're serving company.
After removing as much of the chicken meat as you care to, return the bones to the crock pot. It helps if you separate the bones or mush them to make it lie flatter. Add enough water to come 1/2 way up the bones. Turn your crock pot on LO for 8 to 12 hours.
Strain the liquid from the crock pot and refrigerate. Dump the solids into the trash. After the stock has cooled, remove the hard fat from the top and discard. Freeze the stock or use it within a few days.