like the title said i just got done replacing the engine in this thing and went for a drive hit the 4 wheel drive 3 button design on 2000 chevy blazer and 4 hi and lo would only blink checked cable and its good also widow fogged up no defrost coming out vents i think it is a vaccum issue anybody know if both share a vaccum line kind of odd both went out at same time

sorry ment 4 button type also need to service the a/c sytem its drained right now

 

The heater controls are vacuum controlled, comes from rear of manifold, to a T-splitter, one off to the controls through the firewall, one to the vacuum air tank in the left front fender. The vacuum in the resevoir in the fender, this hose often rots off.
There is a vacuum actuator under the battery that can crack/split on the bellows, it should move and pull the mechanical cable which can gunk up and need lube to move as enough vacuum is applied.

 

How many times do the lights blink? my guess would also be that vacuum line because the same line controls both the 4WD and your air

 

they both just continusley blink i will look at the vac lines today and post the results later thank guys

followed the lines all are dryrotted my canister was is the rear bumper but my lines up front run from the actuator to some solenoid under the hood by the wiper motor and then to a bundle on the driver side by the abs computer into the firwall and back to the pvc valve by the engine going to replace all hopefully works .

 

The canister near the rear bumper is the EVAP canister, not the vacuum reservoir. The vacuum reservoir is located in the driver side fender between the brake booster & the ABS pump. A hose should run from the same fitting that the PCV valve connects to on the intake plenum to a check valve / 'T' assembly. One leg of the 'T' will run to another 'T'. The three ports now will run to the front axle actuator located on the firewall near the distributor, into the firewall for the HVAC system, and to the vacuum reservoir in the fender.

 

well its a 2000 chevy blazer 4 button i checked all vaccum and cable everything is fine with that i hit 4 lo or 4 hi here a loud click from the control module and light just blinks i can get it in 4lo but it still blinks and not 4 hi im sure its the module now pulled the plugs and got some water out of it tried cleaning and no effect any buddy got a wiring diagram or way to make sure this is it. before i go to oreily and pay 219.00 for it.

 

First thing... Please keep your threads together. Posting of duplicate threads may result in one or both of the threads being deleted. Repeated offenses could result in the removal of your posting privileges. Please familiarize yourself with the rules of the forum as you have been found in violation of a number in your short time here.

Second thing... Punctuation & capitalization GREATLY help those of use that are here to help read your post. I for one don't like to decipher what should be written in plain English with proper punctuation & grammar nor do I really have the time for it. I know I'm not alone in that so do yourself a favor and make it easy for everyone to read your post. You might just get more/better responses if you show a little effort on your part.

Third thing... Search is your friend. As is the Tech Article (DIY) Index post which is linked to from my signature below, stickied in the Tech Article (DIY) section, and linked to on the forum home page in the Tech Article (DIY) section description.

If you haven't figured it out yet, the 4-button switch means you have the NV236 transfer case. Wiring diagrams can be found in the aforementioned index.

*Merging back into the original thread on this topic*

 

I just had this problem the gear box shifted in to low 4WH 4WL even neutral but would blink forever till I put it back in to 2 WH
It ended up being my front dif wasn't kicking in and there isn't much to that system
4WD Actuator Valve
This is on the firewall up at the top middle it has 2 vacum lines and a 2 prog plug

Follow and replace what ever vacume lines need to be done
1 of the lines go to a t-valv over buy the driver side fender and in to the fender to what feels like a scrwe
its not a screw its a vacum nipple for a vacume chamber the other vacum off of that t-valv gos in the fire wall

now the other line from the Actuar valve gos to the 4WD Actuator
This is under your battery tray if the line is bad replace it
now test your Actuator make sure it holds vacume (I sucked on the line it held good no leaks but it didnt move)
but the 4WD Actuator Cable was frozen
So I removed the cable from the Actuator and it worked great
I found that the cable was frozen from battery acid I replaced the cable took me 30 min and now my 4WD works great
Its a comon problem with the battery leaking on the cables an vacum line

 

Swartlkk sorry for the double thread did not meean for that searched for my other one and it was not on the site at the time. I'll make sure it does not happen again. Thanks for correcting me.

OK guys I have checked the actuator cable and it is not broke. The diagphram holds vaccum while sucking on the line. While it is hooked up to the system it only collapes a little bit and does not move. So I replaced all vaccum lies in the engine bay and still the same. Hopefully I can get to the rest of the vaccum lines that run over the transmission. I also took the computer that is on the kick board out and found some water in the connector but no corrosion there must of catch it early. I'll have to try the vise grip method that Swatlkk posted and see if that works

Thanks for the help guys

 

Being the 4-button NV236 system, you do not have vacuum lines for the front axle running back to the transfer case. The valve is electronic & mounted to the firewall. You might want to try swapping the vacuum lines top to bottom on the valve & see if that changes the operation.

If not, do you have a vacuum gauge (fairly cheap at most autoparts stores & good to have around).