97 Chevy S10 4wh H not engageing

I had my truck inspected & they had to replace the Idler arm. Ever since my 4wh H (electronic engage) clicks when I hit the button but will not engage. Also, I have a steep hill to climb traveling home every time I get close to the top my AC center vents go to defrost. I'm not sure if these problems are related but they started at the same time (I also had to have my emergency brake cable replaced for Inspection).

I have taken it back to the place that worked on it and they can't find the cause for either problem. I bought an AC control at a junk yard (Grade A) didn't help the AC vent problem. Could it be the round black part that holds the vacuum (mounted to the hood).

My plan is to have a trany shop take a look at the 4wh. I really do use it every day to climb my steep gravel driveway. I've had several people ask me what do you need 4wh for this time of year.

Thanks,
Gary