How to test A/C Compressor

Hello folks.

Asking in here as my car shares the same platform as a Fabia and shares the same engine etc as the vRS.

While away in Germany a couple of months ago we were sat in a traffic jam with 30c temps outside. A/C was blowing icy cold. I then spotted a little smoke coming from under the bonnet.

Stopped the engine and got to the side of the road. Lifted the bonnet and couldn't see anything. Engine ran again ok with no more smoke and all seemed fine.

Got back in the car a realised the A/C was no longer blowing cold.

Pressing "Econ" makes no changed to the engine rev or sound when previously there would be a slight change in tone as the load was applied.

Leading up to the failure I had noticed an intermittent whine that seemed to go when the "Econ" button was pressed (A/C off).

What checks can I do to see if it's the compressor, clucth or wiring etc?

If the compressor needs replacing is it DIY-able? No way do I want to pay for labour as I can get a new compressor fairly cheap.

Phil