Thanks All
So here my thinking...
The tester just hooked up to a pressure gauge, and told me its not a "leaker", next job was to find the fuse, on doing this the fuse for the blower was found to be getting so hot it was melting the holder. So we pulled the fuse. The tester (50 years in the industry inc 17 years w124 ownership), said best to get a auto electrician to sort out an external fuse box for blower before you get a engine bay fire, I agreed. No charge for test.
On the way home, my thoughts turned to the cause of the over heating, my blower had been noisy for a while...so time to pull out the blower and have a look.
Im glad i did. The old unit would turn but with resistance, i.e you couldnt spin the hamster cages freely. Also, my pollen filters were full of sycamore seeds and muck, yet more resistance in the system...
I have also, serviced the wiper, and took all the plastic weather proofing out, serviced cleaned and painted.
So, if (BIG if) the ac and blower are on the same circuit, could it be that the extra amps drawn by the blower has fried something in the ac electrical side, i.e. a relay or control box...could be a likely cause?....I say this because the AC 3 weeks ago worked fine for demisting...so am thinking more electrical cause than mechanical for the moment.....