Moisture Problem in R410A Refrigerant

The problem being experienced relates to multi-zone inverter units where the outside (condenser) unit consists of a master unit with two fixed compressors and one inverter controlled compressor plus a slave condenser unit that has one fixed compressor and one inverter controlled compressor. Seven evaporator units are connected to these condensers.

I was called in to assist (by the South African agent for these units) in tracing the problem which was causing these units to lock out on protection which was basically indicating an electronic control malfunction. The factory (overseas) was also convinced one of the control boards (main control board or inverter board) was faulty.

My tests of the system revealed that the inverter board had developed a fault on the IGBT output stage but when I checked the compressor I found that although the windings tested out OK the windings were down to earth (<40KΩ to earth). The manufacturer requires a minimum reading of 10MΩ to earth!

I advised that the R410A charge be removed and then the system evacuated and then the vacuum broken with dry nitrogen until a satisfactory reading could be obtained indicating that the system was now dry. A standing vacuum test after this would confirm that the system was leak free and dry. They were cautioned against applying any voltage (even multi-meter) while under vacuum.

Subsequent to drying the insulation test with a 500v Megger indicated >200MΩ.

The system was recharged with the correct amount of new R410A and is now operating correctly.

My question is this - the R410A charge was released into the atmosphere and I believe that is incorrect and the charge should have been recovered (either for drying or disposal)? Any comments on the procedures for this?

The problem could have originated from several different causes because the condenser units arrive pre-charged and the installation only requires additional refrigerant to be added for the field installed piping which has to be calculated according to a prescribed formula - was the factory charge contaminated by moisture?

My suspicion is that this problem arose during installation because the installation technician failed to follow correct charging procedures and probably did not draw a proper vacuum in the first place. The average technician here in SA (around the world?) seems to neglect this important aspect of an installation and very few use (or even have) a good quality vacuum gauge.

The problem is not restricted to the one installation and we have found that other installations in other towns (same manufacturer but different contractors) have the identical problem.

Controls have been put in place to prevent a recurrence of this problem but the testing and drying of the installed systems is ongoing at the moment.

I would appreciate any input from the CR4 community specialists on their experiences regarding this problem.

Regards, Keith