I've had a similar problem.
See this thread. More questions, than answers, I'm afraid. What I do know is that there is something in my ABS system that gets wet, and when it gets wet, if the A/C compressor is engaged (as it in in either the A/C or defrost HVAC positions) the ABS fails. After a few days, the component dries out, and everything is fine again. What the A/C compressor has to do with the ABS, or with this failure thereof, I do not know.
