2002 S10 4X4 vacumm operated actuator under battery

Hello

New to the forum.
I have a 2002 Chevy S10 Crew Cab LS 4X4. 4.3L V6 automatic. 4WD system works fine, but not sure if the 2WD operation is functioning as designed. 4WD high works, 4WD low works, 2WD works. All the lights on the 4X4 switch located on the dash, light up properly when pressed for the desired operation. I can engage the 4X4 system and hear and feel the solnoid in the transfer case operate correctly. My concern is the actuator under the battery has constant vacumm going to it, which engages the cable to plunger in the front axle. Meaning the front axle is engaged but NOT the driveshaft from the transfer case to the front axle. Even though the vehicle is in 2WD and I have not switched over to FWD, the front axle still has vacumm going to it, which means the axle is turning.
My question is; should the actuator under the battery have constance vacumm? If not what could be the problem.
Appreciate any help/input  

No, you should not have vacumm all the time at actuator. There is a switch(not electrical) in the transfer case that turns on the vacumm to the actuator when you switch to 4x4,this switch is stuck in the "on" position. Trace vacumm line to it and replace switch. This is a common problem with S10's.  

Thanks for the info. Appreciate the help  

I have the same problem and have located the switch on my transfer case.
I am wondering if the constantly engaged frontend has damaged anything.
I blocked my truck up and let someone engage the 4x4 with the truck running
while I pulled out on the plunger that the vacuum bladder and cable pull on.
The front axle still didn't engage. What does the wiring harness plugging into the cable mount on the front axle do?