If the pressure is too low, then the risk is that the compressor can burn out. It will then be unable to compress the refrigerant from liquid to fluid, which will see your car AC unit grind to a halt. If the pressure is too high, it could burst the compressor causing a leak of ...
So turn on your A/C compressor and see if one of those fans comes on. Then the other one will be for the radiator. As far as no heater/hot air. I am assuming that is because there is no hot coolant circulating in the engine. When the engine is warm, feel both upper and lower ...