I cleaned out my rear valve block 5 years ago, and replaced some of the o-rings from the local hardware store. It was full of dessicant powder. Still works fine. C1A20-64 = pressure rising slowly. I've had that code several times. Once was due to a bad voss fitting in the front valve block, another time it was a bad compressor, another a cracked dryer, and recently leaky pressure swiitch.