Is it the compressor or the inverter at fault?

If you get an error on your air con or heat pump indicating inverter fault / over current etc, (there are loads of fault codes for this) they all mean the same thing. Either the inverter PCB (printed circuit board), the Compressor, or both are knackered. The skill is to work out which one is at fault. Manufacturers will have their own convoluted solutions, some will sell you expensive tools, mine works on every manufacturers kit no matter how big and its cheap.

In fridge parlance we call a compressor "the pot". I used to have a coin with pot written on one side and board on the other, toss the coin and change the one it lands on, if it didn't work change the other too.

This is not far removed from the advice given out to engineers, mostly by people selling parts and idiots. I was always told a bad engineer changes everything, a good engineer only changes the broken bit.

If you know your inverter theory you can take a multi meter and bell out the PWM module on the inverter board to see if its knackered.

But its a bit of a faff and I haven't got time here to tell you how its done.

Likewise the compressor, you can bell it out using a multi meter and a Megger

But who has a megger on the van? and no meter tells you if the compressor is seized or tight.

Years ago you used to be able to buy inverter checkers, a box you plugged the compressor leads into with 6 flashing lights. Total waste of money, they dont work. The inverters are so fast these days they spot the box isn't a compressor so no lights, light up.

So how do I do it?

Simple, lets assume we go to a unit with an inverter fault code, we dont know if the fault is that the compressor is faulty or the inverter is not sending out a proper power supply to the compressor.

I turn off the power, wait 60 seconds so all the boards on the unit have powered down, pull the cables off the suspect compressor and put them onto my trusty little compressor from an old (but working) unit. I just plonk the test compressor on the floor in front of the unit. Mine is a 3kW split system compressor. see top photo. The tubes are bent over almost sealing it up so it doesn't leak oil.

Now I turn on the unit and wait for the compressor to start, I stand at the outdoor unit while I wait. As soon as it spins up, I kill the power with the isolator. I only want it to run for a few seconds,10 at most. If the compressor starts the inverter pcb in the unit is good, the fault lies with the compressor.

If the compressor fails to start and the unit trips on an inverter alarm the Inverter Pcb is faulty and needs changing.

Simple huh? just put another good compressor (or any 3 phase motor) in place of the suspect compressor and test it. Its cheap, it works, and its easy to do.

Its good to remember, faulty compressors dont instantly kill inverter boards, it takes quite a long time for a compressor to kill a board, and these days the inverters are so good they will stop the unit before the compressor has time to do real damage. to the board.

And Faulty inverters dont kill compressors.

Enjoy. Who needs fancy tools when you've got an old compressor from a unit you've ripped out on the van?