Arkansas HVACR NewsMagazine May 2025 Issue

HVACR NewsMagazine May 2025

Tech News

Charging Basics To set a proper charge on an A/C system, you must first know the type of metering device. The piston/fixed orifice type system primarily uses the superheat method, and the TXV/EEV primarily uses the subcooling method. When setting a charge, it is always preferable to set the charge in cool mode. Whether you set the charge in heat or cool mode, you should always follow the manufacturer's recommended charging specifications. This section will discuss manufacturer-recommended charging and some indicators that you have set a proper charge in heat mode. But first, there are some things that trump these guidelines and should make you stop and perform more diagnostics. A properly running A/C system with indoor and outdoor temperatures above 68 degrees will have a suction saturation above 32 degrees (freezing). Don't leave a system with a below 32˚ saturation suction without performing more diagnostics, even if the superheat/subcool looks correct. If you see a liquid line pressure that is more than 30 degrees saturation above outdoor temperature (like a 440 PSI liquid pressure on an R410a system on a 90-degree day), do not proceed until you have further addressed the possible causes of high head, regardless of what the superheat or subcool might be reading. Always purge your hoses to prevent introducing air into the system, and never mix gauges when using low-loss fittings if you're working on systems with different types of refrigerants.

Charge in the liquid phase (tank upside down) and add the refrigerant slowly and carefully to ensure you do not flood/slug the compressor with liquid refrigerant. You can do this by watching your manifold sight glass or using a special liquid-preventing adapter, such as the Imperial 535-C Kwik Charge.

These

precautions

will

prevent

causing system damage. Also, at a minimum, perform a full visual inspection of the equipment, including: • Filter inspection • Checking the blower wheel • Checking evaporator coil • Checking condenser coil cleanliness • Making sure the system is wired properly and running in the correct mode