Hi Guys.

It’s that subject of Inverters again. I confess I am hopelessly lost on this subject. Give me a reciprocating single phase relay/cap start/run comp, or a straightforward 3 phase comp and I am in my own backyard… But what about Inverter comps? All this stuff about changing AC to DC and back to simulated 3Ph AC ? frequency modulation and what part do all the electronics play, and the 1500uf capacitor ? I have contacted major distributors with specific problems (compressors trying to start, or locking out) but they are only suggesting the trial and error methods of diagnosis (try a new PCB). It is not cost effective as we all know, and if we have integrity towards our customers we need positive information to provide positive results. No one seems able to explain how an inverter works, or more to the point how an engineer is supposed to test the equipment… I currently have one customer with several Mitsi inverters (3 years old ) givimg similar fault codes, the basis of which being "Fault on outdoor board/compressor fault/locked rotor" etc.. There are instances where I have heard the compressor trying to start (and failing)... The capacitors (3 x 560uf) are soldered to the outdoor board and therefore not easily checked or replaceable, and yet a few hours later the unit starts. (I stress this has not been due to a local overheat situation in which the thermatrip has operated). What can an engineer do to check ? Most of us are only mildly connected to the electronics side of refrigeration circuitry, yes we can recognise transformers, capacitors, diodes, IC's etc, but who can tell us how to easily check the boards ?

HRP, a well known distributor in the UK recently offered this advice from their tech dept. "If the comp isn't starting take the leads off and connect to a known good 3 phase motor or other Inverter compressor in order to check the board"... Surely there must be a more scientific approach than this ?