Blowing out condensers and getting covered in black shit, I remember it well. We used to use R22 to clean out the coils as it would most likely be at hand and R11 cleaned everything else including your overalls, that was before regulation was brought in.
Back to your original problem, Daz, if you needed to link the low pres switch to run the comp, it means that the system was almost completely out of charge, (you need some liquid in the system to maintain the standing charge pressure for a given temperature). If you look for the nameplate telling you how much should be in there, then compare it to how much was in the tin you bought and weigh the rest on some kitchen scales it should give you an idea of how much charge you've now put in. Don't forget to take into account the weight of the tin itself (should be listed as 'tare weight').
Unfortunately, your gas charge has probably escaped through the gland seal of the compressor. When they run dry of oil from lack of use, they get damaged and will always have a slight leak, so don't be surprised if it's out of gas by next summer.
BTW, it's actually illegal to put gas into a system that has a known leak on it, I've been out the fridge game for a few years now, but it used to be £5k and 6 months inside, someone may know if its changed!
Another BTW, just got home in my daily drive, a 530 BMW, stuck a thermometer on the vent, it's 30.2 C outside had the a/c on max with half fan speed and it was reading 17.6 C. so I think we can say its a good measure of how well it's running. Going to sit in the garden for half hour to defrost!!
