If you use a vacuum pump to evacuate the refrigerant system inorder remove moisture and contaminates, does it actually create a vacuum or negative pressure within the system? My manifold gauge definitely reads negative pressure but I am wondering if the vacuum pump is just making the pressure in the system lower than atmospheric pressure. Atmospheric pressure is roughly 14.7 psia at sea level, so my theory is that the vacuum pump just lowers the pressure within the system below that which is atmospheric pressure outside of the system, which in fact is not a negative pressure, but in a sense yes it is a vacuum but only because the pressure in the system is lower than that outside of the system. It just seems to me if you actually went below 0 psia then you would be creating a black hole. Can anybody explain this to me?