What is a 4 wheel drive actuator?

I have a 2000 chevy blazer. Im trying to fix the four wheel drive on it. It runs really bad. when i accelerate it hesitates. I took the 4 wheel drive fuse out and it runs so much better for some reason. before i replace the actuator i wanted to know what i does. what parts should i check or replace to fix my 4 wheel drive. Im going to replace the selector switch and if i have to the transfer case motor. is there something im overlooking. thank you|||Hard to say for sure, and I'm not that familiar with Blazer, but on Jeeps they used to have a vacuum hose connected to the front axle, near the middle, that used to get knocked off all the time. Worth a shot to check before you go buying expensive parts you might not need.|||You are probably looking at a major expense to repair the 4WD system. A common cause and simple fix is to see if the vacuum hose slipped off the vacuum tank located under the hood. On my 97 it is a black ball attached to the underside of the hood; yours is probably similar.