Let's talk thermostat controls

[Jolly Roger VX'er]

I was always under the impression that they have the AC compressor run with the defroster in order to simply cycle it so it doesn't stay idle for too long a period and seize up. Since AC usually only gets used during "hot" weather...and goes unused the rest of the time the compressor can rust or seize up. By cycling it once in a while such as during defrost..this tends to keep it freed up. My Bronco used to say in the owners manual to lock the hubs in once a month to get the grease to permeate the hub and keep it freed up for when you really did need to lock in the manual hubs!