4WD button blinking but NO 4WD '99 Blazer
 

My 4WD has always woked and yesterday went to switch (on the dash) from 2WD to Auto 4WD or 4WD and it won't complete the transfer. The light will simply blink for about 30 sec and then go back to 2WD. Could this be a low transfer case oil level?

I did stop and switch to 2WD Lo and it switches the transmission but I'm not certain that it is in 4WD as the 2WD light also stays blinking. Things seem to click like they used to, but it doesn't complete the transfer by having a solid 4WD light. And I do not get 4WD to the wheels.

Any thoughts? I have a '99 Blazer ZR2

ADDED: I also note that my AC/heat is stuck in the vent mode...does this make a vaccume leak more likely? Where should I start to look?

I'd start at the solenoid on the firewall, probably need somebodys help to hit the 4wd button to see if it switches. It has a hole in the bottom that sucks air through it in 2wd and it will stop in 4wd cause it redirects the vacuum to the actuator. If thats ok next try the actuator (its under the battery) to see if its stuck or possibly has a torn bladder. I've had all the common blazer 4wd problems and its never effected my heat control vacuum.

yeah basically my air blower works to blow air but I can't direct where the circulating air goes. It comes essentially out of the vents, floor vent and window vents all the time.

That's why I think that they may be tied to the same problem as both require vacuum.!

Found the problem, simply a vacuum line unplugged. Fixed both problems!!