In the desert which A/C vent to use? The outside air vent or the inside circulated vent The temperature is usually 95 early morning, 100 @ noon, 105 late afternon. Humidity maximum 20% this time of year–usually less.
When the AC is on, the setting should be on recirculation.
I would use recycle most of the time. Start there and then try otherwise and see what you like.
I assume that you are looking for a fast cool-down. If you parked in the sun use the outside air initially with the AC on to blow out the hot air. If you really have 20% max RH, you won’t have a latent heat load at all. (That is HVAC-speak for removing water from the air.) When the inside air is cooler than outside, switch to recirculate.