Is it possible that the vacuum pump that runs my climate control and my esof could be getting weak? At first I had defrost only and my 4wd would not engage. I pulled the double line off of the solenoid and clamped the line coming from the pump. My climate control then worked so I figured that the vac lines going to my hubs were bad. They were very dry rotted so I changed them. Now my 4wd engages but sometimes it takes a while and the same with my climate control it will sometimes take a while before it will move off of defrost.

 

Do you have a Mighty Vac to test components and find possible leaks? How long does your vacuum pump run?