I never really go off of weight unless it's a complete evacuation, and even then I still use the gauges to see what's going on. I have seen systems that are low have a slightly warmer output on one side and have also seen that with a blend door that's not seated all the way. I would check both blend door actuation and make sure you are looking at your high side pressure too so you can make sure you don't have an obstruction in the orifice tube or something.

Jeff