96 Blazer 4X4 issues

[Scotty89]

I have a 96 blazer that the 4X4 stopped working randomly. I have replaced the vacuum diaphragm under the battery cause it ripped. It worked for a while and then it quit again. There is vacuum there. Just seems like there isn't enough. Also and i think they are related somehow but when i pass someone the vents go to defrost. I know there is a vacuum line running back to the transfer case to a switch i haven't checked it yet but i was just wondering if anyone has any known concerns on this.

Thanks

[procaddytech]

Check the vacuum lines going to the vacuum reservoir ball and the ball itself. It should be bolted to the left side of the hood. The vacuum line disconnects sometimes from opening and closing the hood. May need to lengthen the line/hose. You definitely have low vacuum if the hvac mode switches to defrost under load.

[maxisp2000]

There's a vacuum switch on top of the transfer case that breaks. The diaphragm breaks inside which allows transfer case fluid into the vacuum lines. Then there is insufficient vacuum during heavy acceleration.

[Scotty89]

I took a quick look at the hoses leading to that switch. I didn't see any cracks or breaks. I did go ahead and order the switch. For $11 I didnt think id be out much. When i pulled the hoses off the switch there was a little fluid run out. Before winter hit i would have to pull the hose off the actuator under the battery and drain the fluid out of it. Ohh and the hoses leading to the ball on the hood. They all seemed fine too

[maxisp2000]

You had fluid in your vacuum lines. You need to purge or replace all your vacuum lines. The vacuum motors may fail if the fluid has gotten to the diaphragms. Check the vacuum bottle for leaks. If it leaks it's pretty easy to repair with JB Weld. If you can get it all out, your AC should act right, and your 4X4 should go into gear.

[procaddytech]

Warning: Do not blow the vacuum lines out at the switch when you replace the switch or you will blow up your brand new servo diaphagm! I have made this mistake. Lol..

[Scotty89]

I replaced the switch on top of the transfer case. Its still doing the same thing. The vents switch to defrost under load and still no 4X4. Im gona hook a smoke machine up to a vacuum line and see if it comes out anywhere.

[procaddytech]

Here is your vacuum diagram. The best place to hook a smoke machine would be at the engine vacuum fitting hose. Or, using a gauge, check vacuum readings starting at the engine vacuum fitting and working your way back to find the loss of vacuum. If vacuum is good at the fitting and low at the reservoir then you know there is a leak or restriction somewhere. If it is low at the fitting, check for carbon build up at the intake. The check valve could have a piece of hose debris restricting it, etc. Measure engine vacuum at a good source such as the brake booster to get some readings for comparison.

[Scotty89]

Just as a update. I smoked the system today. And so far i found a bad vacuum hose connection at the vacuum tank. And found a pin size hole in the vacuum actuator under the battery. Replaced the actuator and the hose and problem still present. Noticed that the cable running down to the front diff is kinda hard to push and pull. I have an extra cable I'm going to try. And upon further inspection the vacuum diagram above isn't exactly how mine is set up. I have an electric cruise control motor. On the hose from the intake i have a check valve and there are two outlets from the valve. One goes to the tank on the hood and the other runs down and then splits again and one hose runs into the firewall on the drivers side, I'm guessing for the HVAC doors, and the other runs back behind the motor down to the transfer case from what it looks like. I can clamp off the hose running down to the transfer case and my vents will still switch to defrost. So that tells me the problem isn't below.

[Scotty89]

Another update. I have good vacuum down to the transfer Case. but not alot comeing back to the actuator. I unpluged the switch on the transfer case and air pressure tested the hose from the switch to the actuator under the battery and i didnt hear any hissing. I did notice that i cant hook the switch in the transfer case up and move it around and it will change the amount of vacuume at the actuator. So i do have to do something to that vacuum connector on the transfercase switch. I havent had the chance to check the lines at the HVAC control head to see about fluid or anything.

[Scotty89]

Finally got it working. Ended up putting another switch on the transfer case. I smoked the vacuum line from the actuator to the transfercase and had smoke coming from my vent hose. I ended up hooking the vacuum lines directly to the switch in the transfercase, the rubber connector didn't fit the switch very tight and was creating a hell of a leak.