Keys to a Successful Multi Zone Mini-Split Installation

Here are some important things to remember when installing and operating a multi zone mini-split.

What is the minimum number of fan coils required to properly operate this equipment?

Most manufacturers require at least two fan coils to be installed before operating equipment. Even if system expansion is expected in the future, the minimum number must be installed from the beginning. Make sure to check and maintain all minimum required clearances on fan coils to any obstructions such as walls, ceilings, floors, and furniture. Air re-circulation caused by improper clearances can be a real problem.

Know your piping length limits.

Each system will have a maximum total piping length and a maximum single zone piping length, which is the length of liquid line to each zone. As with most mini-splits, a multi-split will also have a minimum piping length per zone that must be followed. This is the shortest allowable pipe length required for each zone. Use the fan coil piping size to select the line sizes. The multi-zone CU (condensing unit) will include flare adapters shipped with the CU that will be used to adapt to fan coil line sizes.

Most multi-zone systems power the indoor fan coils from the outdoor CU.

It is important to use the correct wire size and type. 14/4 stranded is the most popular wire and is required by most manufacturers. Take great care in assuring wire connections are the same on the indoor fan coil as they are in the CU. L1 from the CU should be connected to L1 at the fan coil, L2 to L2, terminal 3/S to 3/S and ground to ground. All 4 wires must be connected. Accidentally applying line voltage to the communication terminal will take the main circuit board out. Care should be taken to never splice or break in any way the “3rd” wire, the DC communication wire. A break of any kind in this “3rd wire” (including switches) can result in a communication error. Ensure that the wires from zone A of the CU follow the line set from zone A to the same fan coil. The crossing of the wiring between zones is a common mistake often made while installing multi-zone systems.

When making piping connections, always follow proper flaring techniques and use the flare nuts shipped with the equipment. Torque wrenches must be used on the flare nuts to prevent over or under tightening and leaks. Pressurize all lines with 550 lbs of dry nitrogen or according to the manufacturer’s recommendations. Weigh in any additional charge if the liquid line exceeds pre-charged line length. Check the pre-charge line length to determine if refrigerant needs to be added. Mini-splits are critically charged and can only be charged by weight.

After starting the newly installed multi-zone system always double check the fan coil wiring. Turn each fan coil to cooling one at a time. Make sure the fan and refrigeration start on that fan coil. Shut it off and move to the next fan coil and repeat. If only the fan comes on or only the refrigeration comes on check for crossed wires between zones. This check should be carried out with all multi-zone mini-split installations.

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