1988 s10 vacuum?

Just bought a 88 S10 with 4.3. I finally got it running after new fuel tank and fuel pump. Now I have found that the 4wd does not engage. The lights on lever light up. I have read that this is probley a vacuum problem. My hvac will only blow out of defrost. Could the 2 problems be linked together, or do you think they are separate?

They very well could be connected. You need vacuum to move the heat to any position other then defrost, and you need vacuum to engauge the front axle. Look for a leaking or missing vacuum line.

Thanks for info, I will work on it this weekend and let you know what I find.

Make sure the check valve, near the back passenger side of the engine is good. That and the vac valve on the transfer case. And the actuator itself. The HVAC could be a different problem, but maybe connected.

I agree with duke...check for any disconnected vac lines under the hood...the vac line in question has a check valve in it.

If the above reveals nothing, check the vac switch on top of the xfer case...most likely stuck open and that also causes the xfer case fluid to be drawn up into the HVAC system and cause both conditions U have. Remove the vac hose at the switch and see if fluid is present...if so, replace the switch, top off the fluid and try to blow out the vac hoses as best as possible.

I found 1 vacuum hose broke off so far. I was able to cut off bad area and place back on. Truck runs and idles alot better. After I replaced it I could hear vacuum leak behind vent control inside cab. I pulled it out enough to stick fingers inside. If I hold over 1 seal for a few seconds it seals off and starts blowing out of ac vents. Do you think I need a new ac motor or can this be repaired? Would the vacuum leak cause truck to burn more fuel?