They don't but they should. I'm not a feeder driver but I recently had this conversation with friend who is in feeder in NYC.
I also think the 26ft straight jobs should have them also. The doors to open all the way like a package car. It's awful.
The reason the yard birds (yard dogs, yard spotters, yard mules etc.) don' t have a/c is that the shifters would keep them running all the time.
UPS does not like wasting the fuel.
The shifters are supposed to shut off the yard birds after they hook and when they drop.
a/c would not help except to blow some cool air on the spotter when the yard bird is running.
They are not running long enough to cool the cab.
Not supposed to be running while they wait for their next move.