I don't know if the Enclave's fan runs constantly when the A/C is on or if it is controlled by a pressure switch, but if you park it with the A/C on, the fan has to kick in at some point or the head pressure will go through the roof. You should be able to see and hear the fan coming on. If it is not coming on, do NOT sit in traffic or parked with the A/C on as this can cause damage to the system. The fan system will be fused and most likely have some sort of relay as well. The fuse will be a high amp fuse of 30 or more amps and probably a large style fuse under the hood. If it is blown, I would "guess" the fan might be faulty or going in that direction. If you have the driver's handbook, it should have the fuse and relay locations. Good luck.