[fanworks]

This is a common feature and goes back a fair ways. My 1990 does this, but I found a way to get it to run defrost without turning on the A/C system. (Push in the defrost select button, then once the vaccum switch has selected it, pull it back out. The buttons only push into select to pulling the tab back out does nothing other than disengage the electric switch for the A/C system to cycle.