I have one on my 05 - works nice - there is a non adjustable 30 sec delay for the diesel (well either instant or 30 secs) - once its running, AC wil start to cool/heat as needed (make sure you save it of when you get out)
Took most of the day for me to install - if I had to do again I would have had the dealer do it for $225 - good instructions but PITA splicing into the ECM