Refrigerant charging is the process of adding the correct weight of gas to your Heat Pump System for peak performance. Most of our outdoor units come "pre-charged" for a specific length of Line Set, usually 25 feet. If your lines are longer than the factory limit, a licensed technician must add more gas based on the Technical Data. This must be measured using a precise digital scale to avoid overcharging, which can damage the compressor. Our MRCOOL DIY systems eliminate this step with pre-charged quick-connect lines. For Professional Grade units, an accurate charge is required to maintain your Warranty Policy. A properly charged system is the only way to achieve the advertised SEER2 efficiency.