Push the AC button in either economy or max mode and hot air comes from the dash vents. Push the defrost button and cold air comes from the dash vents. (the temp 'dial' always in the max. cold position).

I know it sounds backwards - it is working backwards. I think that it must be something haywire in the pushbutton unit.

To compound the problem, yesterday I started the car and now everything is back to normal - defrost button gives hot air to windshield vents, AC buttons deliver cold air to dash vents. I didn't do anything at all to correct the situation, but for the time being it seems to be working fine. I am looking for a pushbutton unit just in case. Maybe the connections inside the unit are damaged.

Thanks for the ideas.