How to Test the Inverter Module on a Ductless Mini Split (Video)

There are several causes for a malfunction of the inverter module (IPM) on a Bryant/Midea ductless mini split, including:

  • Valves Closed (double check all of them)
  • Restriction to flow (cap left on or kink in the line)
  • Shortage of charge
  • Wiring mistake
  • IPM malfunction
  • Outdoor Fan Motor
  • Compressor Fault
  • Outdoor PCB

Watch this video for a demonstration on testing the capacitors and bipolar transistors of your unit.

Use this troubleshooting flow chart – and remember, don’t skip any steps!

Check incoming voltage with voltmeter. Between L1 to L2, it should be between 187 and 253 Volts AC. If voltage is outside of these parameters, that will need to be corrected first. A mini split voltage monitor is recommended, especially when the location has higher voltage.

The IPM has two main parts:

  • Bridge rectifier which converts AC to DC voltage
  • Insulated Gate Bipolar Transistors (IGBT)

Remove the unit cover and control box cover, then restore power to the unit.

Check for DC voltage at terminals P+ and N-, at the capacitors:

  • Should be around 300 volts +/–
  • If there is no voltage, the rectifier is bad and you should replace the IPM
  • On smaller units the IPM is part of the Main PCB

Moving on to test the IGBT, first disconnect the power from the unit and allow 5 minutes for the capacitors to discharge before beginning this test.

Failure to do so may cause system damage or cause electrical shock!

To test IGBT set your meter on Mega ohms. Place one lead on the P+ terminal, at the capacitor.

Place the other lead on:

  • U and record your reading
  • V and record your reading
  • W and record your reading

Take the lead off of the P+ terminal and put it on the N- terminal.

Place the other lead on:

  • U and record your reading
  • V and record your reading
  • W and record your reading

Are these readings close and consistent? If so, the IPM checks out; if not, replace the IPM.

If the IPM is good, other options to test include:

  • Fan motor
  • Compressor
  • Check the Compressor jacket for discoloration or burn markings, this can be an indication of overheating
  • You may end up needing to replace the main PCB.

Contact the experts at B-Y with any questions!

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