I have been searching the net for hours and can't find any anwers anywhere to this.

I have a 2000 Chevy Blazer with the auto switch on the dash and the vacuum switch on the firewall not the transfer case. I noticed the other day with the hood up I could hear a wicked vacuum leak. I found it was sucking air in the vent hole on top of the vacuum switch on the firewall. The service 4 wheel drive light was coming on every once and a while so I figured I found the problem and replaced the vacuum switch. The new switch does the same thing and now the front axle seems to stay engaged. I have never heard the vacuum switch leak like this ever before when I had the hood up. Anyone have the firewall vacuum switch and have noticed theirs doing this?

I am really growing to hate the 4x4 system in the Blazer. It never seems to work right for very long.

 

lol join the club, ive owned about 3 of them before finally buying my fourth and throwing all that stuff in the garbage and putting a front axle out of a k5 blazer cause i got so sick of that stuff failing.

it is possible that the lines are crossed at the switch. there should be constant vacuum going to the switch then when 4x4 is engaged it opens that switch sending vacuum to the front actuator. theres a third line coming out of that switch that is a vent. so maybe the vent and return line are crossed.

 

As it turns out the two vacuum lines were switched (thanks abig84). If you have the vacuum switch on the firewall like me the line going to the vacuum pot under the battery tray goes on the top port and the line going to the vacuum reservoir in the drivers side fender goes on the bottom port. When they are hooked up correctly there is no vacuum leak through the vent on the vacuum switch. Now for the strange part I had that switch replaced at the dealer July 2011. I am not sure when the lines were switched but the 4 wheel drive will work with them switched, it just doesn't work well. The front axle stays locked well after you switch out of 4 wheel drive and of course the vacuum leak. It definately switches in and out of 4 wheel drive crisper now with no sticking effect on the front diff. Hopefully it works for another few months now.