In theory, air conditioning systems are designed to never leak refrigerant, meaning they never need to be charged. Of course, we all know that isn’t the case and there are times a system loses refrigerant due to leaks or poor maintenance.
Aside from setting airflow, refrigerant charging may be the least understood practice in the HVAC industry. Yet, except for using a different refrigerant, charging an R410A system is the same as charging any unit. There are several methods to choose from, but there’s typically only one correct method for the unit you’re working on.
The fundamental steps for refrigerant charging are the same for all systems
- Confirm the system’s been properly installed and evacuated. A proper evacuation is crucial to a unit’s optimum performance.
- Clean key components. All coils, filters, blowers, the condenser, and the evaporator must be thoroughly cleaned. The blower must be able to move the correct amount of air.
- Set the required airflow. The correct airflow must be set to the manufacturer’s recommended settings, typically 400 CFM/Ton +/- 10%.
- Identify the type of metering device. Different systems have different types of metering devices. Fixed devices mainly use the superheat method and the TXV device uses the subcooling method.
- Vent hoses and manifold before installing gauges. This helps avoid introducing air into the system.
- Add refrigerant. R410A refrigerant is always added to a system as a liquid (unlike R22 which may be added in liquid or vapor states)
- Seal the system once the charge has been set.
Methods for Properly Charging an R410A System
Space doesn’t permit a detailed explanation for each method, but this basic guide covers the methods that can be used for charging an R410A system.
- Superheat charging requires monitoring the saturation temperature of the low side suction gauge, the actual temperature of the low-pressure suction line, and the indoor and outdoor temps entering the units.
- A unit with TXV (thermostatic expansion valve) is designed to maintain a constant superheat and controls the amount of refrigerant released into the evaporator. A low charge gives a low subcooling and an overcharge gives a high subcooling and high compression ratio.
- The weight or “weigh-in” method is one of the quickest and most accurate methods of charging. It can be correctly performed under any ambient conditions.
- The pressure and ODA temp method is pressure and temperature-driven and commonly used for initial charging. The manufacturer typically supplies a chart that is specific to the unit being charged and it should not be used on other units.
- The approach method is required by Lennox units. “Approach” refers to the difference in temperature between the liquid line leaving the condenser and the air entering the condenser. It does not require attached gauges but does require a good temp reading on the liquid and suction lines.
Most if not all manufacturers have charging charts available for their units.
Properly charging an R410A system doesn’t have to be complicated. Think of refrigerant for an HVAC system like you do antifreeze for your car. Under or over fill it and your car won’t operate at its best. For best results, just remember to thoroughly read the manufacturer’s specs, understand the unit you’re working on, and carefully measure and calculate, since an undercharged or overcharged system will result in poor efficiency, capacity, and reliability.