Connect the indoor air handler and the outdoor condenser through the numbered terminal block exactly as marked on the equipment panel. Terminal 1 usually carries the line conductor, 2 the neutral, and 3 the communication signal between the two units. Use a 14–16 AWG stranded copper cable rated for 600 volts and route it through the wall sleeve alongside the refrigerant lines. Each conductor must land on the same number at both units; mismatched terminals interrupt control communication and prevent startup.
Feed power from a dedicated breaker in the service panel directly to the outdoor condenser disconnect box. Most residential systems require 208–230 volts single phase with a breaker rated between 15 and 30 amps depending on capacity. From the disconnect, run the supply cable into the outdoor unit terminal block marked L1 and L2. Tighten terminal screws to manufacturer torque values, usually around 1.2–1.8 N·m, preventing overheating at high load.
Route the control cable between units away from high-current conductors such as compressor supply leads or electric heaters. Maintain at least 50 mm separation inside the conduit path. This spacing reduces electrical noise that can disturb the communication circuit between boards. Label both ends of the cable before termination so service work later does not require tracing conductors inside the wall cavity.
Mitsubishi Mini Split Wiring Diagram for Indoor Outdoor Unit Power and Signal Connections
Match the numbered terminals between the indoor air handler and the outdoor condenser exactly as printed on the equipment terminal strip. Terminal 1 normally carries the line conductor, 2 carries neutral, and 3 carries the control signal between boards. Use a 14 AWG or 16 AWG multi-core cable rated for 600 V insulation. Each conductor must land on the identical number at both units; mismatched positions interrupt communication and the compressor will not start.
Power Feed From Breaker Panel
Run a dedicated supply from the electrical panel to the outdoor unit disconnect box. Most residential systems require 208–230 V single phase with a breaker between 15 A and 30 A depending on cooling capacity. From the disconnect, route L1 and L2 into the condenser terminal block. Tighten screw terminals firmly so copper strands sit completely under the clamp plate; loose connections create heat and insulation damage during compressor startup.
The indoor air handler normally receives operating voltage through the interconnecting cable from the outdoor section. Because of this design, no separate supply is needed at the indoor location for many models. Verify terminal markings on the indoor block before attaching conductors, since the power pair and communication lead share the same cable sheath.
Control Signal Conductor Routing
Place the communication conductor away from compressor power cables, electric heater lines, or inverter drive leads. Maintain at least 50–75 mm spacing inside conduit runs. Electrical noise from high-current circuits can disrupt board-to-board communication and cause fault codes related to signal loss.
After completing terminal connections, restore power and observe startup behavior. The indoor fan should initialize first, followed by condenser fan and compressor after a short delay of 2–5 minutes. If the system fails to begin this sequence, recheck terminal numbering, conductor continuity, and tightness of each screw terminal.
Terminal Block Connections Between Indoor Air Handler and Outdoor Condenser
Match the numbered terminals between the indoor air handler and the outdoor condenser exactly as printed on both connection strips. Terminal 1 typically carries the line conductor, terminal 2 the neutral return, and terminal 3 the communication signal between control boards. Use a 14–16 AWG stranded copper cable rated for 600 V insulation and route it through the wall sleeve alongside the refrigerant lines.
Strip each conductor approximately 6–7 mm before insertion into the clamp terminals. Copper must sit fully beneath the pressure plate with no loose strands exposed. Tighten each screw firmly; most terminal blocks require torque between 1.2 and 1.8 N·m. Loose clamps produce heat during compressor startup and can trigger system shutdown.
Maintain identical numbering at both units. The conductor placed on terminal 1 indoors must land on terminal 1 outdoors, the same rule applies to terminals 2 and 3. Crossing these positions interrupts the communication circuit between control boards and prevents the condenser from receiving operating commands.
Install the equipment grounding conductor on the marked ground screw or grounding bar inside both electrical compartments. Use a green or bare copper conductor sized at least 14 AWG. The ground path protects electronic boards and metal housings from voltage faults during compressor operation.
Route the interconnecting cable away from compressor supply conductors and fan motor lines. Maintain at least 50 mm spacing inside conduit runs or equipment cavities. This separation reduces electromagnetic interference that can corrupt the low-voltage signal passing between control boards.
After completing all terminal connections, restore power and observe the startup sequence. The indoor fan normally begins first, followed by the outdoor fan and compressor after a delay of about 2–5 minutes. Failure during this sequence usually indicates incorrect terminal placement or a loose conductor in the connection strip.