The previous posters are correct, it is the blower relay. Located behind panel, left of parking brake (AT), Must remove entire plastic panel, not just the access. You will see the fuse panel, at the top and left side of the fuse panel you will see a couple tabs that can be pressed to unlock the panel, pull the panel toward the inside of the car to dismount. On the back side of the fuse panel you will find 4 relays that match Duralast 20578, the top one is the blower relay. I haven't been able to find a diagram that shows them or anything that indicates what each relay is for. I tested by pulling the bottom relay and replacing with the top while the car was running and blower turned on high (but not blowing), no change, took the bottom relay and put it up top, and immediately the blower came on. This caused a check engine light, was read as connectivity network error, will replace the bad (bottom) relay tomorrow and should cure the error.
Symptoms: After warming up car, and driving it for 15-40 minutes, the blower was set on high but would not blow even though vehicle temp was up to normal. The blower would sometimes come on after 15 minutes and sometimes after 30 or 40 minutes or not at all. The part listed at Autozone refers to Duralast 20279 but this is incorrect, you need Duralast 20578 which is listed as rear defrost blower relay(controls main blower as well).
Hopefully this was thorough enough to save someone some time.