I have a heat flow problem. The drivers side defrosters, and vents all blow cold

The heater valve is was more likely what was changed. My thought is if the coolant system full. The dealer should know how to insure it is full, myself have had to remove the upper hose and manually fill the system. The car is full of sensors for every mode of the operating system. I would take it back and tell them it didn't work and give them a chance to make it good (at a discounted price, get an estimate before re-fix), if they won't find someone else that will. They need to guarantee their work as well.