AC Hiccup/Lights Dimming

[Ga_ml320]

When AC is on, Trans in D, car stopped at light (foot on brake) the instrument panel digital readouts will sometimes dim and then cycle back to normal, seems to coincide with an intermittent engine rough idle. I have a new battery, alternator and voltage regulator so it's likely not one of those. Also, when the car is moving the ac blows cold but seems to "hiccup" for like a second where the blower slightly pauses, then goes right back. No problems with cold air really, just these odd issues which all go away if the AC is turned off. 2002 ML320 111,000 miles