This happened to me on I70 in the mountains on a particularly bad day. It was obvious that there was frozen fluid because it would only take 1/4 of a gallon before it was full, and would run out after very minimal use. My tank was fine, it was just the Walmart "-20" rated fluid that was full of shit. Granted it was cold, but more like -10 to 15. I now only run the expensive -32 to -40 stuff. Having a wiper fluid issue on a busy, snowy mountain road is not something that I will be repeating. I was able to get it unfrozen by letting the vehicle idle, allowing the engine bay to heat up a bit, all while constantly running new fluid through it. Total pain in the ass, but when you need to see, you need to see. At home, you could always just heat up new fluid, or even water, to melt the ice. Then run the system until it is dry, making sure there is nothing remaining of the suspect fluid. Finish by spending a dollar more on fluid that will not let you down.