I had a friend tell me that the microcomputer will be tripped whenever you do this kinda thing. If you dont mind the annoying messaging(if your car is equipped with it) I'd say do it coz you will be much warmer and its really functional if you are in the northern states. I'm amazed these werent an option,but then again, by 1999, all Volvo policy was being directed from Michigan hence the lack of such nifty features you'd easily find in Audis or even Jettas that year!