Inverter Mini Split Quiz

Ten questions on inverter compressors, electronic expansion valves, flares and installation. Pick an answer to see whether you are right and why. Related reading: The Code: vacuum.

1. An inverter-driven compressor in a mini split:

   1. Runs at only one speed
   2. Varies its speed to match the load
   3. Changes speed with the reversing valve
   4. Requires a hard start kit

   The inverter changes the frequency of the power to the compressor, letting it speed up and slow down instead of cycling on and off.

2. Most inverter mini splits meter refrigerant with:

   1. A fixed piston
   2. An electronic expansion valve controlled by the circuit board
   3. A float valve
   4. A manual needle valve

   The board drives the EEV from temperature sensor readings, adjusting refrigerant flow as compressor speed changes.

3. On many mini splits, the indoor and outdoor units communicate through:

   1. A separate thermostat cable only
   2. A communication conductor in the interconnecting cable
   3. Wi-Fi only
   4. The refrigerant lines

   The interconnecting cable carries power and a communication signal. Miswiring or swapping conductors causes communication errors, so follow the wiring diagram for the exact model.

4. The most reliable way to tighten a flare nut is:

   1. As tight as possible
   2. With a torque wrench set to the manufacturer's specification
   3. Hand-tight only
   4. With thread sealant on the flare face

   Under-tightened flares leak and over-tightened flares crack. A properly made flare and the manufacturer's torque value are what seal the joint.

5. Before making a flare, the tubing end should be:

   1. Cut square with a tubing cutter and deburred
   2. Cut at an angle
   3. Crimped
   4. Left with its burrs to seal better

   A square, clean, deburred end makes a smooth, even flare that seats properly. Burrs and uneven cuts cause leaks.

6. A mini split line set longer than the factory pre-charged length usually requires:

   1. No adjustment
   2. Additional refrigerant per foot, as specified by the manufacturer
   3. Removing refrigerant
   4. A larger outdoor unit

   The outdoor unit ships charged for a set line length. Longer runs need the extra charge per foot listed in the installation manual, weighed in.

7. Why do many techs avoid connecting gauges to a mini split that is working properly?

   1. Gauges cannot read inverter systems
   2. The charge is small, and every connection loses refrigerant and risks contamination
   3. It automatically voids every warranty
   4. The pressures are too low to read

   Small charges are sensitive to losses. Diagnose with temperatures, error codes and the manufacturer's procedures first, and connect gauges when the diagnosis calls for it.

8. The indoor unit is flashing an error code. The best first step is to:

   1. Replace the board
   2. Look up the code in the service manual for that exact model
   3. Add refrigerant
   4. Reset it repeatedly

   Error codes are model-specific. The service manual explains what the code means and which tests to run.

9. In heating mode a mini split periodically runs a defrost cycle. During defrost:

   1. The system temporarily reverses to melt frost off the outdoor coil
   2. The indoor coil freezes
   3. The compressor stops for good
   4. Refrigerant is vented

   Frost on the outdoor coil blocks airflow. The unit runs in cooling mode briefly to warm the coil, and the indoor fan usually stops so it does not blow cold air.

10. After installing a mini split, before opening the service valves you should:

    1. Pressure test with nitrogen, evacuate and confirm the vacuum holds
    2. Open the valves immediately
    3. Add extra refrigerant
    4. Run the unit for an hour

    The line set and indoor coil must be leak-free and dry before the factory charge is released. A nitrogen test and a vacuum that holds confirm both.