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The Importance of Proper Grounding with Mini-split Installations

By Gerry Wagner

Are you grounded? I have been concerned…VERY concerned…about what I call “mystery issues” which come up with inverter based mini splits more often than is acceptable. You all know what I’m talking about…erratic compressor operation, inaccurate setpoint maintenance, premature component failure and other issues which often times have no obvious cause. I see piles of control boards returned as defective that when replaced, still had the same phantom problem as before.

Gerry Wagner
Gerry Wagner

If you have attended my troubleshooting class you know how I feel about changing boards…it rarely is the answer.

Here is what my research has found:

  • The grounding system is the reference point for all computer logic based equipment…like inverter based mini splits! That board that we keep blaming…well it may indeed be the source of the problem but replacing is NOT the answer!
  • That board my friends is a micro-processor…YES…A COMPUTER! It has all the benefits of a computer but it also has all the vulnerabilities and weaknesses of a computer.
  • Within computers and computer based equipment, the internal computer circuits use the ground as the reference point for processing data. If the ground reference for these devices is not correct or “stable” then system reliability is compromised which can cause component failures and “mystery issues.”

The key issue related to grounding that most often cause problems which negatively impact system reliability is current is present on the home’s grounding system.

This situation typically occurs when a wiring error is present within the electrical panel or a junction box such as the neutral and ground conductor wires are junctioned together, or worse yet, they are connected together on the same bar within the breaker panel. This ground current can cause system component failures and “mystery issues” from unstable ground reference conditions within the equipment.

Beyond the fact that the boards in inverter based mini splits are computer based, we also have to consider the inverter process that takes place.

I’m going to dumb this down…not for your sake but rather for mine!

Inverter equipment takes the Alternating Current AC that we provide to the L1 & L2 connections of the outdoor unit and converts it to a Direct Current DC voltage.

In an AC circuit, NO current flows through the ground but in a DC circuit ALL current returns through the ground.

Because of this unique relationship between the AC and DC circuits within the inverter based mini split, the need for proper and stable ground has even more importance.

photo of multimeterPerform an Ohms test across the ground wire from earth to the ground wire going to the equipment…this can be done at close proximity to the ground bar of the breaker panel. You want your test lead to be on the ground wire coming into the panel, (from earth) and the other to be on the ground wire going to the equipment. Be sure your test leads are on the ground wires and NOT on the ground bar of the panel.

If you read 3 Ohms or more, there is a poor ground.

If we start checking for proper ground BEFORE we install inverter based mini splits, I am optimistic that we can avoid a fair amount of “mystery issues” and take the mystery out of some.

Consider this: homes built prior to 1950 were NOT required to be grounded. Now consider where a fair amount of inverter mini-splits are installed…in old homes!

About the Author

Gerry Wagner is the Vice President of HVAC Technical Training for Tradewinds Climate Systems. He has 38 years in the HVACR industry working in manufacturing, contracting and now training. Contact Gerry by emailing and for information on GREE products, visit