This is a dual a/c system with 60 oz capacity. Vacuumed it for 2 hours and charged from a heated drum. After taking in 28 oz, it wouldn't take any more even when reving the engine. Gauges were in the 35-40 and 150-175 range. Air is blowing cold but why can't I put in a full charge? The tank weighs about 14 pounds. Shouldn't that be enough for good flow? Charging with tank upright as a gas.