How to Charge an AC

Craig of AC Service Tech on YouTube joins Bryan on the podcast to explain how to charge an A/C unit. He also discusses his excellent new book.

Before you start charging a unit, you must know about superheat, subcooling, and other means of determining how much charge is already in the system. You must also know how the refrigeration cycle works so that you can tell if the system is operating properly. Other must-understand concepts are saturation and the pressure-temperature relationship.

To start off, you'll want to pull the disconnect on the outdoor unit. Then, get information from the homeowner and check the airflow; check the filter and examine the ductwork before turning the equipment on and using an anemometer to check airflow. When you actually begin to charge the equipment, you want to screw on your hoses clockwise and read your pressures. After you read the pressures, push the disconnect back in.

Monitor the low-side gauge and keep the saturated temperature in mind. Verify the metering device and refrigerant type. Your metering device will determine the charging method; you would use the total superheat method on fixed-orifice systems and the subcooling method on TXV systems. You use those values and compare them to the target values to determine if you are low on refrigerant or overcharged. Then, you add or remove the refrigerant accordingly to reach those targets.

Craig and Bryan also discuss:

  • Well-roundedness
  • Sliding calculators
  • Saturated temperature
  • Service valves
  • Superheat vs. total superheat
  • Frozen evaporator coils
  • Adding refrigerant at different points of the system
  • Line set length
  • Breaking the vacuum with refrigerant
  • Refrigerant Charging and Service Procedures

Check out Craig's YouTube channel HERE.

Learn more about Refrigeration Technologies HERE.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.


9/6/19 at 01:28 PM

It’s “Craig”, not “Greg”, no? 😉



To continue you need to agree to our terms.

The HVAC School site, podcast and tech tips
made possible by generous support from