Mini splits are one of the fastest growing sectors in the HVAC industry. Once only found in mild climates, the technology now stretches across the U.S., thanks to advances in inverter technology and zone controls. On the other hand, the level of sophistication in these systems sometimes makes them difficult to troubleshoot when something goes wrong.



According to Paul Sammataro, owner of Plano, Texas-based Samm’s Heating and Air Conditioning, the most common problem his company finds with mini splits is improper installation that results in incorrect charging and/or refrigerant leaks at flare fittings.

“There are occasions when you can visually see oil leaks at fittings,” Sammataro said. “Then we go through our basic troubleshooting like other HVAC systems. You have to know the product and verify proper installation, charging by weight if repairs are done [if the system had leaks].”

Installation requirements per manufacturer guidelines are very important when it comes to properly troubleshooting these systems, Sammataro noted.

“Mini splits can sometimes be difficult to troubleshoot because there are no standards — troubleshooting codes vary from manufacturer to manufacturer depending on the issue,” he said. “Additionally, installation and troubleshooting paperwork is not left with customers. So sometimes, calls to tech support are needed. Less experienced techs will usually have troubleshooting issues.”

Jim Crist, a commercial mechanical HVAC division manager in Salisbury, Maryland, agreed, saying the most common problem with these systems is installation error.

“There is a lack of training because everyone believes it will be a simple installation,” Crist said. “The second most common issue is circuit board failures, which is where a multimeter with amp clamp and oftentimes a phone call to the 1-800 tech number come into play. Diagnosis is based on performance — typically, I always try to perform as many checks as possible before gauges get connected, as the refrigerant charge is critical. Many times, a call to tech support will be required to diagnose the correct electronic failure if that becomes the issue.”

Improper installation, where either the wiring is incorrect or the flares are incomplete, is the most common problem that Bob Dressler, licensed HVAC installer and product expert at eComfort, sees in the field with mini-split systems.

“Incomplete flares or improper sealing will cause a loss of refrigerant within the system and create an error code,” Dressler explained. “You will need to identify the leak. Start the system, and check the fittings with leak detection liquid and/or refrigerant sniffing tools. You can also inject the line with a dye and use a fluorescent backlight to find the leak. If possible, try to avoid hooking up gauges unless it’s a last resort. They will cause refrigerant to leak out.

“Regarding wiring, if the unit isn’t wired correctly, or a single unit is wired to a multi-zone condenser and started, there is a very good chance of the PCB [printed circuit board] going bad,” he added.

Many installers still think of mini splits in the same way they think of old-school air conditioners, Dressler noted. Instead, installers need to start thinking of mini splits as high-tech pieces of electronic equipment.

“Essentially, a mini split can be thought of as a computer with a compressor attached to it,” he said. “To effectively troubleshoot a mini-split issue, you need to call the manufacturer to get to the bottom of an error code. Wait times can be excessively long, especially during peak season, so I recommend setting an appointment via email for a phone call while on-site.”

The last thing a contractor wants to do is make multiple trips to a customer. Getting a ticket number while talking to the manufacturer helps escalate the issue versus having to do the same thing repeatedly, Dressler explained.

“It’s relatively simple to narrow down a mini-split problem, but troubleshooting it can be difficult due to the sensitive electronic equipment involved,” he said. “It’s not a simple air conditioner. Installers should convey to homeowners the importance of periodic maintenance and cleanings to help prevent mini-split problems from surfacing in the first place. It’s also important to convey to homeowner clients that mini-split installations are not DIY [do-it-yourself] projects. To maintain the factory warranty, they must get them professionally installed.”



As Dressler mentioned, preventative maintenance is absolutely key in mini-split systems and can often lead to problems if ignored or put off. Logan Marshall, an operational specialist at Parker Heating & Air, Dobson, North Carolina, said the most common issues he’s found are lack of maintenance and refrigerant loss from fittings.

“I start like a normal residential service call,” Marshall said. “I begin by talking to the homeowner about issues being experienced, then first move to the controller. Seven out of 10 times, I have found it to be an operator error here. Most manufacturers have complicated setups that lead to a lot of tech teaching or operation in a wrong mode. Next, I run a test on the indoor unit to be sure I have fan operations and no restricted filters or coil. Then, I move outside to test pressures and read any codes on diagnostic computer boards. From there, depending on all things evaluated, I find solutions to repair said issues and present to owners.”

Rick Boucher, technical advisor, Comfort Supply Inc., Pittsburgh, said regular maintenance on mini-split systems is critical — perhaps even more so than on a traditional system.

“This tends to get overlooked on these systems because they are so reliable,” Boucher said. “Filter maintenance is critical, as many of the indoor heads work with a lower static pressure than a conventional system that they cannot overcome. This leads to decreasing efficiency and higher energy costs much faster. Debris in the outdoor unit can also impact efficiency but can cause premature equipment failures as well.”

Boucher used inverter drives as an example.

They create a lot of heat, which is dissipated through a heat sink normally in the condenser airstream. Debris on the heat sink can lead to overheating and premature failure of circuit boards.

“When these systems are installed properly, they really are very reliable,” he said. “Just like any other traditional system, there will be failures. Leaks, wiring issues, circuit boards, sensors, etc.”

Boucher’s advice on how best to approach troubleshooting these systems is simply to get trained.

“Knowing how these things operate goes a long way in being able to troubleshoot them,” he said. “In our classes, I stress that the basic electrical flow is the same for our Mitsubishi M & P series mini splits as it is in the City Multi Products. The technicians already have the troubleshooting skills, they just need to know how to apply them to our products.”

League City, Texas-based Vanderford Air Inc. has a lot of mini splits in its service area, according to Chris Crawford, service manager.

“One of the biggest calls we get is water coming out of the supply vent,” Crawford said. “That can be caused by a couple of different things. These units are small on purpose, and a lot of times, that means the blower wheels themselves can get dirty, and the evaporator coils can get dirty simply because air filtration is not as suitable as we would like it to be.”

In cases like these, going back in and cleaning the blower assemblies and evaporator coils becomes imperative, he noted.

Because these systems don’t run like a unitary system with all the electronic expansion valves and thermistors taking temperatures and readings, Vanderford Air has invested in the D-Checker tool, which plugs into a laptop and the system itself. The tool is able to read all of the parameters on one computer screen, so technicians can really see what is happening.

“If need be, we can send all of that data to the manufacturer as well, and they can inform us on the problem, based on the data they are seeing,” Crawford explained. “It comes down to really understanding the unit and the principles behind it from an installation and troubleshooting process. It also comes down to having the right tools — like the laptop and D-Checker. These are high-end systems — they’re very complicated and electronically driven. You have to have the training and tooling to be able to work on them; otherwise, it’s impossible to diagnose them properly.”

Publication date: 2/4/2019

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