Replacing Calipers

Most bleeders look like the photo ... with a spring loaded ball bearing. You might try sticking a sturdy wire down the bleeder ... maybe something is stuck. Or to make sure it is the bleeder and not something else ... take it totally out and see if you get any fluid at all coming out of the caliper. That can be a bit messy so be prepared with a way to catch the brake fluid.
Good luck on your troubleshooting

first off make sure that the caliper you received is the correct one then remove the caliper bracket with the caliper then remove the bolt which holds the flex hose resecure it back on the new the same way you took it off, then put the brake caliper back on and once everything is back together then open the bleeder screw and allow the fluid to gravity bleed through the caliper, you will have to open the master cylinder resevoir cap so that the fluid can flow through the line and into the caliper, alow this to happen for a couple of minutes then close the bleeder valve and have someone get into the car and press down on the brake pedal while you open the bleeder valve again to get a steady amount of fluid to travel through the caliper. do this a couple of times to make sure there is no more air in the system only then could you put the tire back on the murano

was the bleeder screw at the top of the caliper cause if they gave ya one for the wrong side and the bleeders at the bottom of the caliper you ll never get the air out of it

You will need a larger sized C clamp to slowly push the caliper back into its boot. Make sure your brake fluid reservoir kid is OFF,..allowing for the fluid to go back into the reservoir. Once you have placed the C clamp around the caliper, take an old brake pad and place it across the round piston...place part of the clamp over this pad and tighten the clamp..Do not place the clamp directly on the piston, you may damage it or compress it in crooked. so place a used pad across it. Push the piston back in untill its almost flush with the boot, making sure no dirt is on the silver exposed piston..u dont want dirt to go back inside the boot. Once its in, refit the caliper to its mount with the new pads.

Raise the truck and remove the tires. Remove the 2 bolts that hold the brake caliper and remove the caliper. Use a large "C" clamp to push the piston back into the caliper. Make sure you open the bleeder valve when you do this. After the piston is back all the way, make sure you close the bleeder valve. Install your new brake pads and calipers back in place. After doing both sides, get in and step on the pedal a few times slowly until you feel the brakes seat in.