Hear 4x4 click but won't engage 98 Blazer
 

So I turned on the blazer but didn't start it.. Opened the door and pressed 4hi and it goes into 4hi without the blinking like I've been reading about..(I have 3 button dash setup). I can hear some kind of movement from underneath. Then I press back in 2hi and again I hear something clicking.. Go back into 4hi but The only problem is it won't engage in 4x4...
1) where do I start?
2) what is noise being made?

When you select 4WD, the encoder motor performs a mode shift in the transfer case. Linkage inside the case depresses a vacuum switch. The vacuum switch sends vacuum to the actuator under the battery tray. The actuator pulls a cable that is connected to the right front axle tube. Inside the axle tube there is a clutch mechanism that engages the right outer axle with the right inner axle. When it engages, it depresses an electrical switch on the axle tube that tells the TCCM that the axle is engaged and you're in 4WD. If the axle engagement switch is not depressed, the encoder shifts back to 2WD.

First thing to check is make sure there is vacuum available at the vacuum switch on the transfer case with the engine at idle. Left side, above and inboard of the front propeller shaft, (drive shaft). There are 3 lines in the vacuum connector, and the connector is keyed so it only goes on one way.

I forgot to mention that only the face vents works. When I try to switch it to floor or defrost it won't switch. Does that help any because I've heard of instances where this might mess with the actuator..

Do you have a picture if the vac hose? In confused as to which of the 3 I need to check. I've heard of trans fluid making its way into these lines

I just found a youtube clips that might help you.

Good video! Notice on the switch he is holding, the button is depressed and stuck in. This will cause the front axle to be engaged whenever the engine is running. Can you say poor fuel mileage?

A vacuum leak, and or fluid in the lines, can cause 4WD issues as well as HVAC air distribution issues. Both systems use the same vacuum source and reservoir.

You can see the vacuum switch in this image:
Attachment 31498

So after replacing that switch what should be my next step??

If that's the problem, it's fixed, drive it! If you throw parts at it, eventually you'll find the problem. All we're doing now is testing stuff to find out what the problem is, then we fix it.... that's how DIY repairs go;)

Firstly check to make sure that you haven't got a vacuum leak in any of the hoses, and don't forget the vacuum canister.
Then spray some contact cleaner on the connections to the TCCM and the 4 way switch.
Remove the battery and the battery tray and then reconnect the battery via some jump leads as the battery will be on the floor in front of the truck and start the engine. Firstly check the actuator to make sure that the rubber isn't leaking and then get a friend to push the 4 way switch while you look at the actuator diaphragm to see if it's moving and to check if the cable is moving or not.

1) where is the vacuum canister??
2) were is the tccm?
3) how do I know if there is fluid in the lines?
4) I replaced the transfer case solenoid and it didn't seem to have fluid in lines as none dropped out.
4.5) replaced actuator and no movement.
5) my vent control doesn't work.
6) thanks for all the help guys