Too little, and the system can be damaged and won't work properly. Too much refrigerant can be even a greater problem. Excess refrigerant washes the oil right off of critical compressor parts. Before we start adding refrigerant to anything, let's check out some other problem areas first. W hatever else we do later, the first thing is to make sure the machine is clean.
Dirt just mucks up all kinds of machinery.
Air flow is critical, too. Any belts, filters, coils and blowers must be clean and working properly. Anything that restricts air flow to or from the machine must be taken care of. It seems silly to say, but make sure the compressor is really running. It will be warm and vibrating slightly.