Re: AC abruptly quit
If the refrigerant gets low enough the PCM will cut off the compressor. How did you check the pressure. It has to be checked with the compressor running. If the PCM cuts off the compressor it has to be reset before it will work again. Either pull the PCM fuse for a few seconds or unhook a battery cable. 75 PSI sounds like it was checked with the compressor off. 75 PSI is too high for a low side pressure and too low for a high side pressure.
Turn on the a/c while looking at the compressor clutch and you can see if the compressor starts. You should be able to see if it is making noise or vibrating. If it is I wouldn't run it any more until you get it checked. If your refrigerant has been leaking, oil leaks out with it. Over time, if you keep refilling without adding oil, the compressor can lock up due to lack of oil. If it seems to be working ok, you could add some refrigerant and see if it starts cooling normally.
94 Z28 A4