Originally Posted by
aircon50
Are the P and N terminals that Andy refers to, the DC side of the rectifier bridges?
Yep
And - is 320Vac normal at these terminals.
Nope. It's then output of the rectifier so around 320V DC for a single phase rectifier or 540V DC for a 3 phase one.
I do not have P and N terminals as such on this LG board, but can easily get to the diode bridge joints.
Should be good enough for testing unless something has gone wrong between the diode bridge and IPM.
Look for the inverter module on the PCB. See if you can follow the compressor wires to help locate it. compressor connections U, V and W are on one side of the chip, above is P and below are 3 N terminals which are all connected together. Page 54 of the manual in IM's post shows the PCB layout. Look at the top picture then the inverter chip is in the bottom left. P on top, then U, V and W and the 3 N's below.
Am I right in assuming that the voltage at compressor will be AC?
Yes - a 3 phase output but actually made up of loads of square waves.
If so, then the SPM is the actual inverter module for compressor control.
Yes, SPM2 on the circuit diagram.
What are the variables at compressor - voltage, frequency, or a combination of both?
Frequency is the variable but your meter will show an average voltage value which will change with the frequency. As time has moved on now some units altered the value of the highest value of the square wave (PAM control - dunno how but would like to know...) then pure sine wave outputs (as plastered on the sales guff) instead but for testing purposes they are all checked the same.