Wiring Of Hvac Heat Pump Electrical Installation Of AC Unit Today, we’re at a customer’s house wiring up a Mitsubishi Electric 15,000 BTU mini-split heat pump. This unit requires a 15-amp double-pole 240-volt circuit. We’ll walk you through installing the disconnect, running the whip, and tying everything into the panel. It’s a fairly straightforward process if you follow a few key steps.
Step 1: Check the Nameplate
Before doing any electrical work, always check the unit’s nameplate for proper electrical requirements. This model is a 234V unit and has the following ratings:
- Ma ximum fuse size: 15 amps
- Minimum fuse size: 10 amps
We’re using 12-gauge electric heat-rated wire (good for up to 20 amps) and protecting it with a 15-amp breaker, per code and manufacturer specs.
Step 2: Plan the Mounting Location
The unit will be mounted to the exterior wall and will run into the customer’s living room. Fortunately, the indoor panel is located directly behind this wall in the basement, making for an efficient installation.
We first drill a hole from inside to the outside to ensure we avoid existing wires and insulation. Always check that your sill plate and wall cavities are clear before proceeding.
Step 3: Install the Outdoor Disconnect
We use an outdoor-rated disconnect box with a built-in breaker. This allows HVAC service technicians to safely isolate power from the heat pump when needed.
- A grommet is installed on the back of the disconnect for the wire entry.
- The box is mounted level to the wall using appropriate screws.
- Always apply a bead of silicone around the grommet to seal it from moisture.
Wiring the Disconnect:
- Ground wire to the ground lug.
- Line 1 (black) and Line 2 (red) to the line terminals on the breaker.
- Connections are tightened securely.
Step 4: Make the Whip
We use liquid-tight flexible conduit (often called “whip”) which is sunlight and outdoor rated. These are cut to custom lengths (this one was about 3 feet).
- Wires are fed through the conduit.
- Liquid-tight connectors are installed on each end for strain relief.
- One end is connected to the bottom of the disconnect.
Inside the whip:
- Red and black wires carry the 240V to the load side of the disconnect.
- These are terminated on the bottom side of the disconnect breaker.
Note: Some heat pumps come with a pre-made whip, but we prefer to make our own for flexibility and control.
Step 5: Install the Breaker in the Panel
Back inside, we work on the electrical panel:
- A knockout is removed from the panel for the incoming wire.
- A plastic connector is used to secure the wire as it enters the panel.
- The wire is routed safely into the panel, avoiding live bus bars.
Installing the Breaker:
- We use a 15-amp Cutler-Hammer (Eaton) double-pole breaker.
- Ground wire is terminated in the ground bar.
- Black and red wires are connected to the breaker lugs.
Tip: We use an impact gun to secure the connections — it ensures tight, secure lugs with minimal effort.
Once connected:
- The cover is modified to fit around the new breaker.
- It is then reattached securely.
Step 6: Voltage Check and Final Wrap-Up
With everything wired:
- A voltage check is performed across the lugs in the disconnect.
- Reading: 246.5 volts — perfect for this setup.
- We mark the panel as “Mini-Split Heat Pump – Living Room” for future reference.
- A couple of wire straps are installed to secure the wire to the wall.
And that’s it — we’re done with the electrical side of this mini-split heat pump install. The HVAC crew will complete the refrigerant and communication connections between the indoor and outdoor heads.
Final Notes
- Always follow local electrical codes.
- Check manufacturer specifications before installation.
- Be cautious when working in live panels — never touch the bus bars.
- Proper labeling and cleanup go a long way for future maintenance.
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