It's actually HVAC/R which is heating ventilation air conditioning refrigeration, but it needs reversed because refrigeration came first, everything else branched off from it, there was a warm winter somewhere around 1850 that caused no ice for the ice houses it forced a need for mechanical refrigeration, as time ran by the other things showed up. (Fun side note) Michael Faraday discovered the principles of electro magnetism, which it what it runs on, he also made the first sheet metal by combining tin with cadmium (I think cant remember right now) but is which what the air runs through in your vents, I'd love to know what he may think about what he helped create. And oh yeah, I have been stuck in the snow with only one tire spinning way too many times, if it aint 4 wheel drive, fuggetaboutit haha :-)