I live in Phoenix, AZ and have an 05 x5 4.4i. I had a similar problem with mine and it was determined that the evaporator is leaking/failing. The car would blow warm air at start up. By the time I drove to the end of the block the AC would start blowing cool air but never as cold as it should be (I had my 02 x5 for comparison with a perfect AC system) I took the car to the dealership and an evac/ recharge was done to the system. They put in nearly a lb of freeon. After a week of using the car they did a follow-up inspection of the AC system to check for leaks. Thats when they determined it was the evaporator. There is a trap door behind the carpet on the side of the drivers foot well. Behind this piece of carpet is where the trap door to inspect the evaporator is. There is one screw by the gas pedal on the carpet and then it pulls straight out. You could probably take the car to the dealership and have them look at this real quick and see if there is significant leakage. Good Luck