Look under the driver side slide (at least on my unit) when opened. There is a push pull valve that sits near the frame and a small 1/8 to 1/4 line that runs up to the refrigerator. You need to open this valve to let water flow to the fridge.
Hope this helps?
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Jim W.
2016 34RL CC; 2008 Ram Mega Cab 2500HD, 6.7L, 68RFE 6 speed, 4X4, Smarty S67, TDR 145K+miles