Hi. So... new guy here...this is my 2nd Blazer 1st one was a late 80's and this one is a '96 Blazer LS 4X4

Here's my Problem:

I bought this truck knowing something was wrong. The 4X4 lever (MANUAL TRANSFER CASE) was stuck and it wouldn't shift into 4WD (I later realized it WAS in 4WD and wouldn't shift OUT of 4 high!)
Also....the HVAC system is messed up and only blows (crappily) out of the defrost.
so.... I start researching...
A lot od info points me towards the actuator cable. Hmmmm... ok... lets have a look...
I pull the actuator and OIL POURED OUT OF IT!
hahahaha
wow... so I google "oil in blazer actuator" and came out with this great write up about how the transfer case seal leaks on these bad boys and how oil gets past the transfer case vacuum switch and into the entire vacuum system which eventually screws up the ENTIRE HVAC AND 4WD systems!!!
WOW!!!!!!!!!
Here's a link to the article: GMC Sonoma & Chevy S-10 Transfer Case Vacuum Switch
Syriously?
So... this appears to be a common problem? yet I found very little info here.
I dunno
Anyway... If I replace the vacuum switch and purge the lines do you think my HVAC controls and 4WD system will be repaired?
Any info GREATLY appreciated!
THANKS

 

All of the trans fluid must be completely cleaned out of both systems, (vacuum lines, reservoir, HVAC mode switch, all of the actuators in the dash, etc etc) and the vacuum switch on the transfer case replaced. This will either fix it completey, or make it possible to finish diagnosing the problem.

 

I took the Tc Vac switch out and it "appears" ok. What did NOT appeart ok is the 3 lines leading into it! They are full of OIL!
But...obvi the switch and seal upstream are bad! I'll replace the switch, clean out the lines as best I can and see what up!

I almost completely taught myself how these 4wd/vac systems work in one night! holy crap!

 

Upon further snooping it appears its not really the switch at fault... but the seal!
I took out my fill plug from the transfer case and BOUT 2 QUARTS!!! of ATF came out!!!! WOW.
Ill put the switch back in clean out the lines, clean out the HVAC controller, 4wd actuator etc and see where I stand.
This is UNREAL!!!!

 

The Internet is a wonderful thing. Two quarts over-filled is about right. Sounds like the t-case has been over-filled for a good long time! I would suspect your vacuum reservoir ball is pretty full of fluid, and possibly the actuators inside the dash. Unfortunately the HVAC actuators on the '96 are not as easy to access as they are in the later models. Hopefully the pics in that write-up will help you find them.

Also, I doubt you'll have much luck with the HVAC controller after this. Both of my trucks, I had to replace them because I just couldn't get the controller clean enough that it would seal well without hissing. You can actually replace just that junction where the colored lines come together, but I went ahead and replaced the whole control panel.

 

The vacuum switch on the transfer case is leaking inside the switch. There's a brass valve that slides with the spring loaded ball, and a couple of O rings, they are what is leaking. Check your transmission fluid level too, it's probably 2 quarts low

Near the top of the transmission dip stick tube there is a vacuum line with a filter on the end of it. Take the filter off and clean it out, along with the line. The line goes down to a Tee and then to the top of the transfer case, then down to the vacuum switch.

 

So the oil in the Vac lines wasn't as bad as I had feared...in fact there wasnt any to speak of! Surprising given the amount of oil in the transfer case!
Where WAS a mouse NEST in the blower motor though!
replaced that...and found a vac leak...and replaced the 4wd vac switch. Now I have the 4wd working but the HVAC is STILL STUCK ON DEFROST!!!! ughhhh
Strting to wonder if whoever built that nest didnt ruin a vac line under the dash!!!!
Anyone know where the actuator sits that directs flow to the vents?

 

PS- I tried a new used HVAC switch from the junkyard already. no go
PPS- Thanks Captain Hook....that helped!

 

Diagrams are here for '97 and older, starting with the ones under the picture of the t-case vacuum switch (scroll down a ways).

 

interesting problem. i have seen the switches go bad causing fluid to go into the lines but didnt cause any other problems, must have caught it early.