Actually, my grandfather used to unscrew the lightbulb in the refridgerator before the sabbath began, so that when he opened the door, it would not cause the light to come on.
It was considered OK for lights to be on timers, and for things like the refrigerator, AC, or heating to be controled by a thermostat. The difference is that you are taking no direct action to cause "work" to be done (having the heat or AC switch on, or having the oven or refridgerator kick on).
Mark
I remember reading or being told about some Sabbath friendly telephones that didn't have buttons for dialing, but had holes instead. The person dialing the phone would insert a pencil or similar object into the numbered hole which would interrupt a light beam. I thought that was very interesting.