Control wiring open ( VRF SYSTEMS )

[Husky250]

I guess most brands use the two wires for commuication with multiple Indoor units and one Outdoor unit. My question is what happens during normal operation the system is running and the communication link opens? Does the entire system fault out? Here is an example: One outdoor and 8 Indoor units connected. The communication link opens between Indoor units 3 and 4 while running. Will Indoor units 1 and 2 still continue to operate? The wiring is still connected to Indoor units 1 and 2? I thought maybe since all Indoor PCB have to communicate with the outdoor PCB as one system the entire system may fault out on communication error.

Thanks for the help!

[Husky250]

Thats exactly what I thought, but I had a gentleman say like in the first example Indoor Units 1 and 2 would still run due to link communication wiring is still connected. The units after that would only fail. His remarks didnt make sense to me. My studies have taught me in the example above all Indoor units are in a network. If the network opens anywhere the system faults out. I wanted to get everyones advice before I argue my point again. Thanks to all for any information that can back up my theory.

[Brian_UK]

Perhaps if you describe the comms link as a circle it may make more sense.

Such as: The signal goes from the master out to no.s 2, 3, 4 etc. A software or hardware link in the last unit then returns the signal back through units etc, 4, 3, 2, 1 .

If the link between units 3 and 4 breaks then the circle is broken and the signal cannot get back to the master.

Possibly if there was a break after unit 3 but unit 3 was modified to indicate that it was now the last unit in the line then the system might work.

[Husky250]

Brian,
I think I understand what you saying. From my weak understanding the comm link has to communicate through the entire system. Not just one direction from master ( outdoor ) to all Indoor PCB. My idea is to find the break. Find the Indoor units that have good link wiring. Re-auto address the master ( Outdoor ) to reflect the the new number of Indoor units connected. Fix the wiring problem. I just need to know the science of how this works to explain to this guy. I thought my answer was right, but I coudnt explain how I know I was right. I welcome all views on this. If I win the bet he owes me some brew. Thanks

[Brian_UK]

Just tell him that "It's what it says in the instructions" and it is out of your control. ;)

[Husky250]

I tried that, but this guys thinks he is the cats meow of control wiring on these type systems. Im having a hard time backing my theory up with my knowledge. If I can explain how it works It will help. Your advice will help me. Thanks brian.

[Thermatech]

With most VRV / VRF systems even if only one indoor unit is cut from the control communication cable while heating or cooling then this would make a big refrigerant flow problem.
Take your example. Unit 3 & 4 are disconnected from communication cable while operating in cooling mode.
But refrigerant is flowing through the electronic expansion valve & indoor coils & getting dumped straight back into the suction ,,,, right,,, yes.
If the outdoor unit was able to continue to run in this case due to the refrigerant bypass at these two units the outdoor unit would have lots of liquid return in the suction line,,, good idea,,, no.

The system design engineers uderstand that if there is a problem with the control wiring & the outdoor unit can no longer get data from some indoor units then anything can be happening at those indoor units & the outdoor unit cannot see. So the outdoor unit is in danger of terminal damage to compressor.
So as a safety precaution the outdoor unit is programed to stop & flag communication fault.
Then before any damage is done the service enginner has to come & look at the system.
This is just one of many many safety precautions programed into the outdoor circuit board ep rom control chip.

This is one reason why its best to use high quality VRF systems from manufacturers who have been developing these system for many years. The design teams have progresively developed clever control stratagies.
The new comers have lots of young university graduates in the design teams but they lack the practical experiance of many years VRF manufacture & development & so the products lack the refinement which come from many years of development & improvment.

[Husky250]

With most VRV / VRF systems even if only one indoor unit is cut from the control communication cable while heating or cooling then this would make a big refrigerant flow problem.
Take your example. Unit 3 & 4 are disconnected from communication cable while operating in cooling mode.
But refrigerant is flowing through the electronic expansion valve & indoor coils & getting dumped straight back into the suction ,,,, right,,, yes.
If the outdoor unit was able to continue to run in this case due to the refrigerant bypass at these two units the outdoor unit would have lots of liquid return in the suction line,,, good idea,,, no.

The system design engineers uderstand that if there is a problem with the control wiring & the outdoor unit can no longer get data from some indoor units then anything can be happening at those indoor units & the outdoor unit cannot see. So the outdoor unit is in danger of terminal damage to compressor.
So as a safety precaution the outdoor unit is programed to stop & flag communication fault.
Then before any damage is done the service enginner has to come & look at the system.
This is just one of many many safety precautions programed into the outdoor circuit board ep rom control chip.

This is one reason why its best to use high quality VRF systems from manufacturers who have been developing these system for many years. The design teams have progresively developed clever control stratagies.
The new comers have lots of young university graduates in the design teams but they lack the practical experiance of many years VRF manufacture & development & so the products lack the refinement which come from many years of development & improvment.

Thank You for such an in depth answer. That makes perfect sense to me. I guess that kind of safety is a good thing in the context as you put it. Thanks !!!!!

[eggs]

Once again Thermatech simplifies science for the masses.
Cheers Therma

eggs