VRF Wiring Guide – D1/D2 & H1/H2 Explained (MBHX MSHX MUHX)
Quick Summary
| Circuit | What it does | How to wire it |
|---|---|---|
| D1 / D2 | Outdoor ↔ Indoor communication | Daisy chain all indoor units |
| H1 / H2 | Wall controller ↔ Indoor units | Daisy chain to all controlled units |
1. D1 / D2 – Outdoor to Indoor Communication
What it is
- These wires allow all units to talk to each other
How to wire it (IMPORTANT)
- Must be wired in a straight line (daisy chain)
- Start from the outdoor unit and link through each indoor
Correct layout
Outdoor → Indoor 1 → Indoor 2 → Indoor 3 → etc.
Key rules
- ✅ Wire unit-to-unit (loop through terminals)
- ✅ Keep polarity the same: D1 → D1, D2 → D2
- ✅ Fit the resistor on the last indoor unit only
Avoid this
- ❌ No star / junction wiring
- ❌ No branching cables
2. H1 / H2 – Wall Controller Wiring
What it is
- Communication between the wired controller and indoor units
When it applies
- Only relevant when one controller runs multiple indoor units
How to wire it
- Must also be daisy chained between all units
Correct layout
Controller → Indoor 1 → Indoor 2 → Indoor 3
Key rules
- ✅ Daisy chain unit-to-unit
- ✅ Match polarity: H1 → H1, H2 → H2
- ✅ Ensure the loop goes through every indoor being controlled
Avoid this
- ❌ Do NOT run separate cables back to the controller
- ❌ Do NOT create star wiring
3. Simple Way to Think About It
You have two separate loops:
Loop 1 (D1/D2):
Outdoor → all indoor units (system communication)Loop 2 (H1/H2):
Controller → all indoor units (control signal)
4. Installer Checklist (Quick Fault Prevention)
Before powering up, check:
- ✅ D1/D2 runs through every indoor unit
- ✅ No breaks or star connections
- ✅ Last indoor has resistor fitted
- ✅ H1/H2 reaches all indoor units being controlled
- ✅ All polarities match (D1-D1, D2-D2, H1-H1, H2-H2)
Common Fault Cause
Most communication faults come from:
- Missed indoor unit in the loop
- Star wiring instead of daisy chain
- Missing end resistor
- Polarity reversed
