Increasing subcooling with an Ac target levels of level pressure and compression ratio, decrease capacity. Targrt, does a Delta T between 18 and 21°F mean that a system has a correct refrigerant charge? Mike Bernier Mike Bernier is the lead content writer and founder of Arcane Eye.

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This is normal for these types of systems. Mini-splits are usually designed to have less superheat in the evaporator coil which allows for more heat to be removed from within the building. Note: These systems have an accumulator tank which safeguards the compressor while the system runs at a low superheat.

To learn more, check out our video on the accumulator tank! So, does a Delta T between 18 and 21°F mean that a system has a correct refrigerant charge? The simple answer is maybe.

Remember, Delta T is only intended to help estimate your overall performance. While a reading between 18 and 21°F is an indication that heat is being transferred well, it does not take into account if the system is operating completely correct.

In the case a system with a piston metering device, you may measure a 19°F but the system could be slightly over-charged and liquid refrigerant could be entering the compressor and damaging it. To determine if the compressor is getting fully vapor refrigerant to enter, measure the total superheat.

If the refrigerant has several degrees of total superheat, the refrigerant is presently fully in the vapor state. The only way to effectively measure the refrigerant charge of a system is with total superheat and subcooling measurements.

Delta T alone should not be solely relied on to determine the refrigerant charge level or for troubleshooting. Delta T should be one of multiple measurements taken when servicing a system in order to get an overall idea of how the system is operating.

Finally, does the Delta T really matter? Stay tuned for our article on Delta T for heating coming out soon! Also check out our Video " HVAC Delta T Explained! What Temperature Should it be? Be sure to check out Our Book and Other Products Here!

Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA.

He is also an HVACR Contracting Business owner of 17 years and holds an NJ HVACR Master License. However, you want to be as close to the target subcooling as possible.

There is a leak that needs to be fixed and refrigerant will need to be added. Some refrigerant will need to be recovered into a recovery bottle.

Also even though we need to check the charge of this unit with subcooling, make sure that the vapor gauge shows a sat temp higher than 32 °F, otherwise there could be a problem such as low airflow, liquid line restriction, or low refrigerant charge that would allow the indoor evaporator coil to freeze.

For now just make sure the vapor gauge reads above 32°F and check out our articles on troubleshooting a frozen evaporator for more info! In the following example, lets determine if the unit is correctly charged, undercharged, or overcharged.

We measure the subcooling based on the picture. Then we compare it to the target subcooling. Since the actual subcooling measured is less than the target subcooling, we would need to add refrigerant a little at a time until the subcooling was the same as the target subcooling.

If this was an existing unit that was previously working fine, then there must be a refrigerant leak in the system. Whenever possible, find and fix the leak before adding more refrigerant. If the system is very low on refrigerant, do not just add more refrigerant because it will likely leak out rapidly from the system which will not be good for the service tech, the homeowner, or the environment.

I use anti corrosive bubble leak detector, and primarily the ultrasonic leak detector when searching for refrigerant leaks. Here are the links for those items for searching for refrigerant leaks:.

P ractice checking the charge with the subcooling method below! If you want to learn how to use subcooling, superheat, saturated temps, and delta T to troubleshoot a problem with a system, check out our book available here on our site and on amazon!

This book goes from the basics all the way through to troubleshooting complex problems. It is designed for those beginning in the field as well as those who are seasoned in the field. Also make sure to check out our HVAC Quick Reference Cards as well as our Refrigerant Charging Workbook!

They are both great resources to give you an advantage out in the field! Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 17 years and holds an NJ HVACR Master License.

Measuring Airflow in CFM Using the TrueFlow Grid. Carbon Monoxide Alarm vs Low Level CO Monitor. Top 10 Gas Furnace Package Unit Problems! top of page. Craig Migliacco Apr 8, 7 min read. The HVAC Subcooling Charging Method, Explained!

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