I have a ford expedition 2007, the rear a/c all of a sudden blow warm air, the front a/c is good, the freon is fully charged, both line going to the firewall are cold, I opened the rear panel and replaced the air modulator, since it was making some noise, but that was not the problem, air does rotate from below and through the upper vents when I do adjust the temp in the rear , looking at the rear a/c unit I see an expansion valve, I can see 3 a/c lines , top 2 are hot and the bottom one is cold, what do you might think is the problem , thanks in advance