Mitsubishi Heavy Industries FDC2501 tech advice required

Hello,

Mitsubishi Heavy Industries FDC2501

I have just registered on this forum to glean some wisdom on an issue I have observed today on a customers Mitsubishi Heavy Industries FDC2501HKXE2 driving six FDTS series head units. The customer has two installations plus many splits. I was there for a six month service and system check.

OK there are no error codes and on the face of it everything seems to be normal. However walk past the FDC2501's and everything is not in order. Ears and visual inspection reveal the compressor (3 phase inverter driven) to be quite violently twisting backwards and forwards on its rubber mountings. On this unit I notice some frost build up on the suction line and I here some gurgling in the expansion vessel. The other FDC2501 is no where as bad with the compressor only lightly twisting on the rubber mounts.

On the first unit I am surprised the pipe work is holding together quite honestly. The rubber mounts have started to disintegrate. I did not have the time today due to long hours and a long drive to pressure check R22 or to pull the charge to see if it is low. This system runs with 14.2KG.

What I did observe though on head unit switch on.
Compressor starts and runs sweetly, current pull (red phase) 7A
Compressor starts to run faster and speed variations is heard. Refrigerant valve opens.
Current pull climbs to 10A, compressors starts its rotational judder with knocking noise from mounts due to violence. Current pull jumps to 12.7A and compressors runs like this.

Other unit as I say pulls about the same total power 13A but the rotational judder is small in comparison.

So what do you guys think?

I think start with the basics, check the refrigerant charge and change the mounts if I can.
Can you tell me best oil type for this system and best recharging method for both refrigerant and oil. Unfortunately I do not know on this system what the normal refrigeration pressures should be, but the presence of light frosting compared with the other FDC2501 tells me that charges are potentially out. I am reluctant to let the customer use this unit as I do not want to loose the compressor or the immediate pipe work. The earliest I can get back to this customer would be next weekend. Meanwhile I need an idea on cost as that will of course be there question and wether or not the work is nesecary.

Help and guidance appreciated!

Thanks, Andrew.

If the system was SOG then you would expect lower comp run amps in comparison to the other unit which is running ok.
The frosted suction could indicate liquid flashing off in the suction line. This could be caused by full liquid to suction bypass in the system.
Perhaps some liquid slugging is the cause of the excessive comp vibration ?

Suggest before recovering refrigerant monitor the system with gauges connected & check cooling performance at all indoor units to make sure no liquid to suction bypass.
If liquid is flushing through one indoor unit then you should be able to hear it & also the cooling performance at the other indoor units will be very poor.

If the system is SOG you will see excessive discharge temp & discharge SH. The compressor shell will be very hot but the suction & discharge pressure will be low.