Mini split units are great at cooling and heating a space and can operate for many years with no issues.
Although they usually work well, one issue that can happen is the refrigerant charge becomes low, and the unit does not work as well as it once did.
When this happens, the unit will need the correct amount of refrigerant added in to operate correctly.
Mini Split Refrigerant Recharge Official Method vs. Common Method
Mini split units are notoriously difficult to have refrigerant added into the system.
Since they have components such as variable speed compressors, the pressures can be very difficult to narrow down and get correct.
Many HVAC techs will add refrigerant in small amounts to get a unit working, but it is not the official method most manufacturers recommend.
The official method for recharging most mini split units is to recover the refrigerant inside the unit, vacuum it down, and add it back in the correct amount by weight.
When the unit is empty, the correct amount by weight is added back in.
The official method will never overfill or underfill a system.
With that said, it is common for an HVAC tech to add small amounts of refrigerant in steps to get a unit working again.
What are Normal Operating Pressures for 410A Mini Split Unit?
Most mini split units with R410a refrigerant will have a low pressure between 117 PSI and 120 PSI.
It can vary depending on the unit, but if the level is lower than 117 PSI, it is usually low.
When adding in refrigerant, the level is usually set to at least 117 PSI, and the inside unit is checked for cold air blowing out.
The refrigerant is then slowly added in until it starts to blow cold air.
Official Method To Add R410a Refrigerant to a Mini Split
- Use a recovery machine and recover any refrigerant inside the unit.
- Fix any leaks.
- Vacuum the system down.
- Examine the face-plate of the unit and read the pounds (LBS) of refrigerant the unit uses.
- Using an HVAC weight scale add in the correct amount of refrigerant by the pounds labeled.
Items Needed to Add R410a Refrigerant to a Mini Split that Has a Low Charge
- HVAC Gauges
- Mini Split Adapter
- Refrigerant
HVAC gauges, an adapter and R410 refrigerant will be needed to top the unit off.
Example R410A Adapter 5/16″ SAE Female to 1/4″ on Amazon
R410A Adapter 5/16″ SAE Female to 1/4″ SAE Male Vacuum Service Port for Mini Split Air Conditioners
Things to Know Before Adding Refrigerant to a Mini Split
- Overfilling a unit will stop it from working and possibly damage it.
- Add in refrigerant very slowly in a short burst and wait at least 5 minutes to see if it is working.
- When adding in refrigerant, you will only be able to get it close, not exact.
- The official method must be used to get the exact amount in the system.
A video is at the bottom of this post for a visual walk-through.
How To Add R410a Refrigerant to a Mini Split that Has a Low Charge
- Remove the cap to the low pressure line (Usually the only port).
- Check the gauges and be sure the valves are turned off (clockwise).
- Connect the gauges center yellow hose to the R410a refrigerant tank.
- Connect the adapter to the blue low pressure line on the gauges.
- As quickly as possible, attach the blue hose with the adapter to the mini split port.
- A small amount of refrigerant will come out, which is normal; simply attach the hoses as quickly as possible to minimize the loss.
- Turn the R410 Tank valve to on.
- Flip the box of R410a upside down so the liquid will flow into the unit instead of vapor.
- With the mini split on and working, check the blue gauge pressure.
- Most mini split units will operate between 117 PSI and 220 PSI, although it can vary.
- Turn the blue valve slowly and let in a small amount of refrigerant (1-2 seconds) and then close it.
- Let the unit run for at least 5 minutes, and then check the inside unit for cold air.
- If the inside air is not cooling, let in a small amount of refrigerant again.
- Continue this as necessary until the inside unit blows cold air again.
- Once finished, Turn off the R410 tank valve and let the mini split pull in any leftover refrigerant from the lines.
- Turn the gauge blue valve off, and as quickly as possible, remove the adapter from the mini split port.
- A small amount of refrigerant will be released; simply remove the adapter as quickly as possible.
Can You Add 410A Refrigerant to a Mini Split?
Yes, refrigerant can be added to a mini split using the low pressure valve.
Most manufacturers have the recommended method as recovering R410a from the system, fixing any leak, vacuuming down the unit, and adding in refrigerant based on weight.
Many HVAC techs will add small amounts of refrigerant to a system that is low, but this is not usually the recommended method.
How Much R410A Refrigerant Does a Mini Split Contain?
Most mini split units contain 2-3 pounds of R410A Refrigerant.
The amount can vary and will be labeled on the face plate of the outside unit.
The face plate will display the amount the unit holds in LB (pounds).