Originally Posted by tinygiant
I just purchased an '04 Excursion Limited. At idle, the air temp slowly builds to outside air temp. Anything above idle will blow cold air. I've not seen this in any other vehicle I've ever owned. I haven't been able to do any troubleshooting as of yet (though I plan to check some items tonight). Any ideas come to mind from the great cloud?
I havenever owned a vehicle that did not do this...
The way an A/C system works is anything from your house to your car is heat exchange. In order to do this effectively, air must be passing over the heat exchanger. The more air passing, the more efficient it will be.
Notice how the exterior A/C unit on your house has a large powerful fan?
At idle you do not have a lot of air passing of the exchanger. At speed you have a lot. Depending on different conditions (temp, barometric pressure, humidity, etc.,) the vehicle A/C may reach a point where is not exchanging heat because the air passing over the exchanger is simply not different in temp enough to effectuate cooling.
You may notice this more in the front A/C than the rear as I do believe the rear has it's own exchanger that is not effected by engine heat.