There are 2 methods that I've seen:
1. CHessMaster's at
viewtopic.php?f=5&t=6042&p=180099&hilit=+switch#p180099 which apparently disables the AC in several modes all the time and
2. kapalczynski's somewhat more elegant solution at
viewtopic.php?f=5&t=52364&p=585766&hilit=+switch#p585766 . UNFORTUNATELY some of Kap's pictures are no longer linked. If you want a copy of the entire post with pictures drop me an email; not a PM as I cannot attach a Word document to a PM reply.
If I was to do either it would be Kap's as it lets you elect to have the AC compressor run or not run. For example there are defrost situations (ex condensation on the inside of the windscreen) where you want the AC compressor on to reduce humidty as opposed to ones where it's not needed (ex. ice on the outside of the windscreen). Hence I'm reluctant to disable the AC compressor function entirely.