Air con testing?

[Mossey]

Ok so the weather is getting warmer I switch the air con button but doesnt seem to get any colder than normal.
The fans are working on the rad at the front but not sure how to check everything else, before I take it to a garage to have the gasses checked I want to make sure everything else is ok.
Had a look in haynes but not much info on air con.
Wondered if anyone has suggestions on how to check?
Will I hear the clutch engage on the compressor by disconnecting the single black wire?
How many fuses/relays are in this circuit and where are they?
Are there any valves or solenoids to check?

[Alchamist]

I would suggest having the gas checked first, as there are many garages around that will check it for free. There is a good chance there is a leak somewhere in the system, though you should be able to hear/feel the compressor engage with the aircon switch.

[Mossey]

Dont hear or feel the compressor engage at all, would this still engage even if gas is low?

[Road Hog]

Basically works like a stethoscope but needs 2 people,
With the engine running put a long socket extension shaft on the compressor pump body & place your ear to it,listen & mentally note the sound/s.
Then without moving your head signal person 2 to switch the A/C on,you should be able to hear the electro-magnetic clutch "come in" & the pump turning.