'84 AC linked to IDLE?

The ac runs great when the compressor kicks on. The optimum word is WHEN. It will work fine and then kick off at a stop light and then won't kick in at all. Anyideas?

Might check your charging system. If theres not enough volts at the compressor, the clutch wont engage. When the compressor shuts off, rev the engine up and see if the AC comes back on. If it does, its a voltage problem.