I have a 2005 Dodge Durango Limited with a Hemi and only 55k miles. The AC used to blow freezing cold, even to the point where it would ice up on long trips, I fixed that with a service bulletin mod, adding a resistor to help the compressor cycle properly, and now on hot days, the AC only blows cool air from both the front and rear vents. All vents and airflow settings work fine. I added a can of freon, but it didn't improve much, the compressor runs constantly and doesn't cycle off like it used to, any idea why it's not getting as cold as before?