four wheel drive not working on 2000 Chevrolet Blazer

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
bought used. four wheel drive stopped working right away. repaired by dealer. not working again. why
(1) Answer
You could try checking the black vacuum line against the firewall, towards the top of the engine bay. If you look at your distributor and look right there are two small plastic fittings for two vacuum lines. i think its the bottom one that controls whether the 4wd engages or not. I'm terrible at explaining things but i hope that helps, my 4wd stopped working after i took it in to get a tune up. I took a look under the hood and saw that had taking off the vacuum line and not put it back on.