If your AC pressure gauges are reading over 150psi with the engine turned off, it's a sign that you might've overcharged your air conditioning system. Although to get a more accurate analysis, you should give it a few hours for pressure to equalize in the AC system. If it's still reading 150psi, you'll need to release pressure by evacuating some of the excess refrigerant/freon. However, you should note that 150psi may not necessarily be the threshold for all cars. Certain makes and models of vehicles may have varying limits for how high or low the AC pressure should be with the engine turned off. So, be sure to refer to your owner's manual, as well.