Daikin failures

I have taken over a large daikin VRV heat recovery install....its a bad install to be sure, but I have a theory I would like to throw at you Daikin guys. I have had several compressors fail, both inverter and standard. None have been burnouts, most were simply over amping or locked down from bearing damage.
These are fairly long lines going down up to 5 stories then down the hall to up to 13 apartments. I have noticed that the tennants seem to be turning off the indoor units, when I hook up my checker I may only have one unit on out of 13, and sometimes Ill walk up to a group of 9 outdoor units and none of them are running. So my question is this; could the lack of runtime be not allowing proper oil return? I know the return cycle is a timer, and I wonde if its not sufficient in this case due to a lot of off time.

Also, only sytems with indoor below outdoor have failed, and only in mild weather when simultainious heat/cool is likely....meaning one suction line.

You say it's a bad install;
are they intsalled within Daikin pipe length/height limits? Are refenet joints horizontal? Additional refrigerant charges calculated properly? Long pipework without OFN purging will leave a lot of oxidisation- posssible if the install quality is poor. Oil recovery sequence will be started by the outdoor unit, and will flush oil back from all connected indoor units, whether they are operating or not.

Oil return is triggered by run time, no?

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Originally Posted by Texaskelly

Oil return is triggered by run time, no?

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2 hours after first switch on and then every 8 (run) hours thereafter

Do you know the model numbers of the outdoor units. VRV system oil return operations are 2 hours after initials power up, if you have had to reset the outdoor units to re-initialise, then it will perform this operation or every 8 hours of accumulated run time, oil return will also be activated. Dependant on the age of the system, VRV systems can also activate more frequent oil returns dependant on compressor output. If say, all compressors were operable, and inverter frequency remained high, the software will allow additional oil return operations based on this high output. When you say the tenants are turning off the units, do you mean power or locally by remote controller. Constant powering off of indoor power may cause the expansion valves to lose their correct placement opening.