M&P The Power Inverter board

Testing the inverter

The Power board or Inverter is responsible for controlling the speed of the compressor. It does this by taking the AC current supplied to the unit and converting it to a 3 phase DC current in a waveform that resembles a 3 phase AC current.

This balanced signal offers an extremely smooth and highly accurate speed control of the compressor without the compromise of energy wastage. This is due to the accuracy of DC current by providing 100% amplitude only when it is required and 0% when not, as shown in green and red on the right image.

Inverter testing procedure

1. Turn the mains power supply off to the unit and wait at least 3 mintes for all of the capacitors to discharge.

2. Disconnect the 3 wires from the top of the compressor and make the ends safe

3. Turn the power supply back on and wait 60 seconds for the unit to re-initialise so it is ready to operate again.

3. Switch SW4 dip 1 to the on position on the main control board to actiavte test run operation.

5. When the outdoor fan starts to spinning the unit is operating and the inverter voltages can be tested.

6. Set your meter to AC voltage and test each disconnected compressor wire individually to neutral whilst the fan is spinning.

If the Inverter is faulty the voltage output will be less than 100VAC or there will be a significant differential between the voltage output across the 3 cables. Example - 176VAC 177VAC 66VAC

If the Inverter is healthy the voltage output from all 3 cables will be a steady balanced voltage between 100-300VAC. All 3 wires will have the same voltage with a small tolerence level of 3 volt differential. Example - 176VAC 177VAC 176VAC