Sounds promising, Richard. I think mine is more serious; one week on from last visit to Kwik Fit and it is no longer blowing cold with the relay bridged. I now think there is a leak that doesn't manifest itself when the compressor isn't running. Kwik Fit's machine showed no leaks, but it checks without the compressor running. I risked putting the guage on it again and (guess what?) it read the same 1.5 bar as before.
I haven't had much time to look at it this week, but I did loosen the filter today and get the electrical connection off of the pressure switch. That looked fine, but I did notice that the filter was very greasy and nothing else down there was, so I'm wondering if there is a leak at the filter or pressure switch and the greasiness is the system oil leaking out. I would have thought though that if there's a leak big enough for the oil to pass through it would have shown on Kwik Fit's machine.
While it was working, I noticed a strange sibilant hissing sound that seemed to be coming through the vents from time to time, and I wonder if this was the sound of the gas escaping somewhere nearer the cabin. I do hope not.
Temperatures are rising and I have two long drives coming up next week, so I'm a bit hacked off with it now.