Got a new one. It's that time a yr when I start using my defrost and heater again. I turned my heater on the other day and noticed that every 20 secs or so that the engine would idle higher than drop back down again. First thing I thought was that it was acting alot like when the ac is running. And sure enough I popped the hood with the engine and heater running and the ac unit runs when the heater is on. I know it wasn't doing that last winter. Anybody know their way around this.

 

I wonder if the ac clutch is starting to stick. Have you tried spraying some wd40 or such on the ac clutch?

 

It's totally normal for the compressor to run with the defroster to remove moisture from the air. It shouldn't cycle constantly, though. Maybe it's a little low on charge?