ECN Forum Forums General Topics of the Trade General Discussion Area A/C buzzing on start up

If a contactor coil doesn't have the strength to pull the contactor closed firmly the contactor will chatter loudly.

I'd find the problem by pulling the cover and either using a stethoscope (which I carry on my truck) with an open tube to track it down or I'd touch all suspects with a long screwdriver pressing the handle against my ear.