Dildoyle99

Hey i gotta problem which from what ive been reading is very common. The 4x4. Now its a 99, automatic, 4.0 and the 4x4 is vacumm. It works then it doesnt. I dont know if theres moisture in it but im gunna park it in a warm garage and see. When i turn radio off and heat and roll the window down and put it in four wheel drive. The dash clicks twice and the 4x4 light comes on and you can hear the transfer case make a "clink" sound but no four wheel drive, doesnt engage. So please someone help me. thank you.