My wife's 550Z randomly died on her and I can't ever seem to recreate the cause but I pulled it into the garage and let it idle. After letting it idle for a few minutes with the hood up I noticed a ticking sound (almost like a relay switch ticking sound). I got in the car to see what the gauges were doing when it would tick and realized that the heater would kick on then about 5 seconds later the car would tick then all power was lost to the a/c unit. Few seconds later it would come back on... then off... and just repeats that cycle. It does it whether it is using A/C or heater... The fan belt has been squeeling for a few weeks now if that has anything to with it (but not squeeling this morning)... Any thoughts?

 

Bad A/C compressor?