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How to Check Refrigerant Level in AC

Technician is checking air conditioner ,measuring equipment for filling air conditioners.

Learn how to check refrigerant levels in AC with our step-by-step guide. Ensure optimal performance and efficiency with expert best practices.


Maintaining proper refrigerant levels in your air conditioner is crucial for its efficiency and longevity. When refrigerant levels are correct, air conditioning systems can cool spaces effectively without overworking.

However, low levels can cause the system to work harder, which leads to increased energy use and potential damage. Proper maintenance helps you save money on energy bills and repair costs while ensuring the comfort of building occupants. In this guide, we’ll show you how to check refrigerant levels in your AC unit to ensure optimal performance and efficiency.

Introduction to AC Refrigerants

During extreme summer weather, the demand for cooling increases significantly. Refrigerants ensure that air conditioners meet this demand by efficiently transferring heat outside. With refrigerants, achieving the cooling effect that air conditioners provide is possible.

Refrigerants work by absorbing warm indoor air. Inside an AC unit, these substances switch back and forth between being a liquid and being a gas. This switching process allows refrigerants to absorb and release heat efficiently.

Please note that some refrigerants are banned or restricted under CARB refrigeration regulations.

Signs of Low Refrigerant Levels

While it’s important to check refrigerant levels regularly as part of your HVAC maintenance checklist, it becomes critical when you notice some telltale signs that your refrigerants are running low. Here are the signs to look out for in your AC system:

Increased Energy Bills

Low refrigerant can lead to reduced energy efficiency, causing an increase in energy bills and fluctuating temperature difference in your facility. If you notice an unexpected spike in your utility bills, check if low refrigerant levels are the cause.

Weak Airflow

Low refrigerant can cause the evaporator coil to freeze. When coils freeze, the result may be weak airflow and/or warm air blowing from the vents.

Audible Hissing or Other Noises

Hissing or bubbling sounds can indicate an AC refrigerant leak. Refrigerant leaks inevitably lead to low levels sooner than anticipated.


Lower than normal levels may cause short cycling. An indication that your AC system is short-cycling is if it turns on and off frequently and at irregular intervals inconsistent with the indoor temperature.

Steps for Checking Refrigerant Levels

1. Turn Off the AC and Remove the Cover

Turn off the AC unit and remove the cover to access the refrigerant level gauge or gauges.

2. Locate and Remove the Access Panel

Look for the refrigerant level gauge. The gauge is usually on the side of the AC unit.

3. Attach Refrigerant Pressure Gauges

Connect the high-pressure side gauge (red) to the high-pressure service valve. Then, connect the low-pressure side gauge (blue) to the low-pressure service valve.

4. Interpret Pressure Levels

When you check refrigerant levels, there’s little to gain if you can’t determine what your gauges indicate. Here is how to check refrigerant levels in AC systems based on different pressures:

  • High-pressure readings significantly above the recommended range may indicate an overcharged system.
  • Low-pressure readings below the specified range may suggest insufficient refrigerant.
  • Ideal pressure levels vary based on ambient temperature and specific system requirements.

5. Add Refrigerant (if Necessary)

Consider adding refrigerant to the system if the low-pressure readings indicate low refrigerant levels. If the high-pressure readings are too high, it may suggest that there is too much refrigerant in the system or that airflow is restricted.

In such cases, you should check for any blockages in the system or confirm if the refrigerant levels exceed the recommended amount.

Troubleshooting and Solving Common Problems

How to Recharge a Refrigerant?

To recharge a refrigerant, locate the service port, typically found along the larger of the two copper lines running to the compressor outside. Connect a refrigerant charging hose from a refrigerant refill kit to this service port.

Then, slowly add the refrigerant. It’s essential to add the refrigerant slowly while frequently checking the pressure and temperature to avoid overcharging. After reaching the recommended pressure level, disconnect the charging hose and gauge. Ensure all connections are secure.

However, before adding refrigerant, start the air conditioning unit and let it run for a few minutes. This process ensures that the system pressure is accurate for a refill.

What Amount of Refrigerant is Necessary?

The amount of refrigerant necessary for an air conditioner depends on the system’s specifications and size. HVAC systems have specific refrigerant capacities, usually listed in the owner’s manual or on a label attached to the AC unit. This capacity is typically measured in pounds or kilograms and can vary widely between models.

A home air conditioner usually requires 2 to 4 pounds of refrigerant. However, commercial units in facilities often require significantly more.

Consult the manufacturer’s documentation or enlist a qualified technician’s help to determine the required amount. They can adjust the refrigerant level to match the system’s requirements precisely. 

Overcharging or undercharging the refrigerant lines can lead to inefficient performance and potential system failure.

How Often Should I Recharge Refrigerants?

You should only recharge the refrigerant in an AC unit when necessary rather than on a scheduled basis.

Air conditioners are designed to operate efficiently with a closed refrigerant system, meaning they shouldn’t need regular coolant refills. If your system requires frequent recharging, that may indicate a leak or another issue needing attention.

That said, checking your AC refrigerant level is an essential task in your scheduled maintenance operations.

What If I Use the Wrong Refrigerant Amount?

Incorrect refrigerant levels can also affect the overall performance of the unit. To avoid these issues, ensure the refrigerant level matches the manufacturer’s specifications. If you’re a facility manager, ensure your maintenance staff receives the proper training to perform this task.

If you accidentally overcharge your AC unit, promptly addressing the issue is essential to avoid damage. The first step is to stop adding refrigerant immediately and turn off the unit to prevent the compressor from working too hard. Only attempt to remove refrigerant or make adjustments yourself if you have the training to do so.

Contact a professional or your maintenance staff if needed. They have the necessary equipment and expertise to safely remove the excess refrigerant and adjust the charge to the correct level. A technician can also check for any damage that may have occurred due to overcharging and ensure that the air conditioner is functioning correctly.

Preventive Maintenance Tips for AC Systems

Preventing air conditioning challenges is much easier with the right maintenance program. Here are some maintenance tips to help keep warm air cool when you need it most:

Change Your Filters Regularly

Dirty filters can reduce the efficiency of your AC. Installing a new filter every month during the cooling season for central and window units where hot air will be most prevalent is recommended.

Regular System Inspections

Conduct visual inspections of the AC unit regularly. Look for any signs of wear, leaks, or obstructions, and verify that all connections are secure. If there are no obvious leaks, an electronic leak detector may be able to spot what isn’t apparent. 

Checking the cleanliness of the filters and the condition of the fins and coils is also crucial for maintaining the unit’s efficiency and prolonging its lifespan.

Check and Maintain Insulation

Ensure the seal between the AC and the window frame is intact to prevent cool air from escaping. Otherwise, cooling your building will take much longer, which may increase both your energy bills and the wear of the air conditioner.

Schedule Professional Inspections

Arrange for professional HVAC technicians to conduct regular inspections. For a home air conditioner, you will need to contact a company; for facilities, you will schedule your maintenance staff as required.

Achieve Optimal AC Performance with ServiceChannel

Following the recommended HVAC preventive maintenance guide and establishing the right program for your facility will help prevent unacceptable temperatures, coolant leaks, and an incorrect refrigerant level. Using the right software will make this part easier.

ServiceChannel can help you keep all heating and cooling units in check. Our preventive maintenance software lets you easily schedule when your team must check pressure gauges or when emergency repairs are needed. 

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