Rear AC comes on by itself? normal?

[Jolly Roger]

Ill have my AC selector knob off and out of the blue my rear AC will kick on all by itself, the light will illuminate on the aux button. Does it have a thermostat?

My AC pump also seems to kick on when on defrost selection. (no light on snowflake)

 

[GreyStone]

AC pumps always come on with defrost