So let my start off by saying, the installation techs installed the valves backwards at first, so I was getting hot water out of my cold, never noticed that until my room mate was pissed at me for washing on hot because it was going to make our electricity go up... So I switched the hoses blue to blue, red to red, now only cold water comes out!! Figured it was the hot water valve/solenoid, so I got a new one. Nope. Same problem. If I set to hot water and turn off the cold water I get a humming noise and no water comes out, or if I keep the cold water valve on, only cold water is coming out. What is the issue?! Is it the technicians fault? Did they screw sensors up by installing backwards? I have a Samsung model WA40J3000AW/A2. Brand new, no clogs or anything that I can gather. valves are clean. water comes out of both pipes when disconnected from the washer at the correct temperature.
If it is delivering cold when you call for hot only then it is opening the wrong valve (assuming your statement that the hoses are correct now is true).
Return the unit, it is malfunctioning and it seems like a controller issue not a valve or solenoid issue.
However; you state that you replaced a "valve/solenoid". Are you certain you did it right? Are you certain you wired it right? If the unit was "brand new" why did you do that yourself instead of having a factory approved technician troubleshoot and repair the unit under warranty?