Branch box
A distribution unit used on some multi-zone systems to split refrigerant and control signals between indoor units. Because it sits between the outdoor unit and several heads, a branch-box fault can present as a problem in one zone only.
Also called distribution box, branch selector
What is a branch box?
A branch box is the distribution unit on some multi-zone systems that splits refrigerant and control wiring from one outdoor unit out to several indoor units.
Branch box: how it works
Instead of running a separate pipe pair from the outdoor unit to every indoor head, one larger run reaches the box and the box distributes from there. That shortens installation pipework, but it puts valves, sensors, and wiring for several zones inside one enclosure that may be concealed.
Where you meet the term
- On an installation drawing, where the box position determines the pipe runs and the access needed later.
- In a single-zone fault on a multi-zone system, where the branch serving that head is part of the shortlist.
- In a service access complaint, where a box in a sealed ceiling void has no practical way to be reached.
How to check it
- Establish which zones are affected. A group of zones failing together while others run normally points at the branch they share rather than at any single indoor unit. Owner check
- Confirm the box location and access route. Handover documentation should record it. Establishing access before a service visit avoids a second appointment. Technician
Branch box: what it is not
- Not every multi-zone system has one. Many run individual pipe pairs from the outdoor unit to each head, so the box exists only where the design used it.
- A branch box is not a junction box. It carries refrigerant as well as wiring, so work inside it needs certification.
Branch box questions
Do all multi-zone mini-splits use a branch box?
No. Many connect each indoor unit directly to a port on the outdoor unit. Branch boxes appear where the design favoured one larger run into a distribution point.
Can a branch box cause a fault in one room only?
Yes. Each branch has its own valve and wiring, so a fault confined to one branch presents exactly like a fault in the indoor unit it serves.
Where is the branch box installed?
Above a ceiling, in a loft, or in a plant space near the middle of the pipe runs. Its location should be recorded at handover because service access to it is needed later.
Where this definition comes from
Written from service manual material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- MXS-W, MXL-W, and MXLH-W Series Engineering ManualDaikin MXS-W, MXL-W, and MXLH-W multi-zone systems, including wireless controller range and interference guidance.