Testing Inverter

It is best to test the inverters with the compressors disconnected especially if you expect the fault is in the compressor.
But if you remove the wires from the compressor and try to run the systems a fault will be displayed:

You will need a digital multi meter with a min max function, Turn off the power
Disconnect the compressor either from the PCB or at the compressor terminals.
Connect your meter to two of the phases (Red to blue) set your meter to record max and min voltage
Power up and Start the unit
Let the inverter start and watch the Voltage rise
Record the maximum Voltage
The inverter will stop after a few seconds and the voltage will fall to 0
Swap the leads to measure the next two phases (Red to Yellow).
Measure as before
Repeat for the last two phases Blue to Yellow.

The readings of maximum voltage should be the same for all 3 measurements if not the PWM is faulty.

If no Voltage is sent out by the PWM check whether the Capacitors are charging, you should measure 320V DC on single phase units and 600V DC on three phase units.
On most of single phase units the PWM and the capacitors etc are all on the same PCB so if there is a fault the PCB will need replacing.
source: Hendrag RE

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