Can't get heat to come in my 2008 ford tarrus?

Can't get heat to come in my 2008 ford tarrus?

First you have to make sure the cooling system is full. With a cold engine, fill both the radiator & the expansion tank to the top. Drive a day or two, then top-off the tank but DON'T open the radiator. Repeat until the tank stays full & see if the heat works better.