2004 ac compressor on/off & buzz sound/smoke from ac compressor

It is unlikely that the compressor itself was smoking, but the magnetic clutch that couples the compressor to the drive belt has been known to go that way! Two others in recent weeks have had AC system failures related to clutch failure, so you are not alone.

Most likely it was getting fragile, which caused the intermittent on & off situation. Do you have a gauge set for determining the maximum acceptable pressure in the system? It is possible that you overfilled it a bit, causing a pressure rise on the high side. The weakened clutch is overtaxed, slips and smokes. The clutch alone can be replaced without replacing the entire compressor, but someone should check the refrigerant level carefully to be sure that you don't wipe out the compressor next.

Would the clutch cause it to buzz and then a puff of smoke? I did fill the ac at the L-cap pressure side of the aluminum tube and had the gauge that came with the can. So only measured from the L cap side.
The weird thing is that before I started to refill, i did notice the clutch engaging and dis engaging by itself before filling. What would cause this?

The compressor should cycle on and off as needed, taking direction from the A/C ECU. That is part of how it regulates the delivery of liquid (compressed) freon to the evaporator expansion valve. You made it sound as though the compressor was off when it should have been on. Without monitoring power to the clutch, how would you know if the system was calling for cooling, or if it was correctly in the 'off' mode?

The compressor itself is a sealed unit, so I doubt that it liberated smoke. More likely it was something electrical.