Mondeo Air con

Apart from checking the air flaps are working, and that the compressor belt is not slipping, there's very little you can check without proper a/c equipment. Get an a/c specialist to look at it. Preferably one familiar with car systems. Mike.

satisfactorilyking correctly. It won't blow cold although it has worked on a couple

As Mike G said, there's not much you can check without specialist equipment.

As a basic test, when you switch on the aircon, do you hear a 'click' from under the bonnet? You should also hear the engine revs dip slightly (momentarily).

If you can get under the car and look at the compressor, you should be able to see when the 'clutch' engages.

Also, check that the fan is working to drive air through the condenser.

If it worked intermittently (and worked properly on those occassions, i.e. became satisifactoriily cold) then it may just be a lose electrical connection?

Cheers

David P