Ok on my 1997 Blazer I have to put my Blazer in Nuetral and if I push the 4Hi the light flashes and stays in 2WD but if I push the 4Low it will flash and engage the 4Low but both 4Low and 4Hi stay on.....Every now and again if I push the buttons at random I will get the 4Hi to engage.

I am thinking vacum leak but not sure because my AC/Heat vent will shift from whatever position I have it in to the top(Defroster vents) on acceleration.

 

It sounds like you might have some wiring issues and/or a switch issue. Have you checked the switch for proper operation (continuity between the respective pins when a button is pushed)? How about checked the connections on the TCCM & encoder motor for corrosion?

A vacuum leak shouldn't cause the transfer case to shift incorrectly at random. It may affect front axle engagement, but shouldn't affect the transfer case shifting.

 

I still have issues and I hear the actuator by the transfer case making noise when it tries to go into 4H........frustrating!!!

 

Sounds like you might have a "confused" transfer case motor. Or like Kyle said, a switch problem. After check the basic things, you could get it scanned and see what the fancy computer box is doing. I had a similar problem once upon a time...motor wasn't fried, but "confused" So I got a brand new used motor and it has worked fine ever since.

 

This link is pretty good:

https://blazerforum.com/forum/tech-a...ill-help-7180/

...especially the last post by Kyle. Takes some time to read through and understand, but there really is a pretty defined diagnostic procedure that should get you to a solution. Beats throwing money at the problem.

 

Also, did you ever get the vacuum leak fixed?

 

Still have the issues with my 4WD and can't find any leaks but AC Vent still goes to defroster on acceleration.

 

Still have the issues with my 4WD and can't find any leaks but AC Vent still goes to defroster on acceleration.

 

SOunds like there's still a vacuum leak somewhere. Only foolproof way I can ever track these down is with a MityVac. Some of those lines, the only way you can see them is by digging deep into the dash. The MityVac at least can narrow down the possibilities before spending too much time.