Results 1 to 6 of 6
Thread: Mitsubishi FDC250VS & four FDT60
-
17-06-2022, 02:07 PM #1
Mitsubishi FDC250VS & four FDT60
Hi everyone,
I have a question regarding our aircon system and hope the fantastic knowledge on this forum can help.
We recently purchased a building that has an aircon system comprised of a Mitsubishi FDC250VS outdoor unit and four FDT60DV ceiling cassettes, the whole system is operated by a single RC-E5
wired controller.
All four cassettes operate within the same floor space, we find that we don't need two of them working and my question is can individual cassettes be disabled or turned off?
Each cassette has a power isolator switch but if I turn off one the whole system stops working, a red LED flashes on the controller.
Many thanks in advance for any help that can be given.
-
17-06-2022, 06:55 PM #2
Re: Mitsubishi FDC250VS & four FDT60
All four need to run together because individual units can't regulate refrigerant, that's done by the outdoor unit. Also outdoor unit is sized to run all four, i.e 25kW outdoors and 24kW (4x6kW) indoors
When you turn one or more off then the system registers a communication error which is those flashing lights.
You could change to a smaller outdoor unit if you can get one compatible but the pipework would need resizing so pretty much a new install I'm afraid.
You could block one (or two at a push) of the outlet vents, might help?
Cheers,
Andy.
-
17-06-2022, 07:39 PM #3
Re: Mitsubishi FDC250VS & four FDT60
Hi Andy,
Thanks for taking the time to reply and explain, much appreciated
My background is in electronics so I was naturally curious to try and find out how these systems worked. I had assumed that the cassettes could control refrigerant but the pipework layout kind of suggested this was not so and you have confirmed that.
The controller shows one master and three slaves, unfortunately the two cassettes that we don't need push out very cold air (closest to outdoor unit) and the two we do need cool ok but not as good (furthest from outdoor unit).
Again, if you could feed my curiousity it would be appreciated and forgive my assumptions...
If the load was only 12kW would the outdoor unit simply not run as much compared to it having a 24kW load?
I thought that in a system like this there might be some way to "balance" the cassettes "refrigerant wise" to compensate for the pipe run distance?
Today I disconnected power, signal line and the controller X/Y lines from one cassette (always experimenting) in the assumed belief that if the controller cannot see the cassette then it will just run the other three.
Silly me! I just get an E14 error message for the "missing" cassette.
Do you know if there is an initial process where the controller "finds" the cassettes? If one cassette could be deleted from the controller I then assume that the system would run the other three but would the 25kW source/18kW load mismatch be detrimental?
Sorry for all of the questions!
-
23-06-2022, 06:56 PM #4
Re: Mitsubishi FDC250VS & four FDT60
Hope that makes some sense. In essence it's probable that two units cool better because the refrigerant flows easier to them (longer runs and more bends to the others = more resistance). Perhaps the branch pipes are spaced too far apart between the furthest units?
To take a unit off requires altering pipe sizes to suit and that assumes the outdoor can run at a lower duty to suit.
Some units you set the ceiling height and this ups the fan speed for a higher ceiling. I had a look but couldn't see that option on those units, only found an old manual so could be wrong there. Otherwise like I say, if you can block of a couple of vents on the closet units might help. Blocking off only one vent seems to be the general advise but I'd imagine you'd get away with two.
Last edited by Tayters; 24-06-2022 at 12:17 AM.
-
25-06-2022, 09:13 PM #5
Re: Mitsubishi FDC250VS & four FDT60
Thanks for taking the time to give such a detailed reply, most informative and I have learned a lot!
Of course in my naivety I have not considered that it isn't a matter of just isolating a ceiling unit electrically, as you have pointed out it is still connected to the pipework and refrigerant would continue to flow through, so there is no advantage in doing this.
I have investigated the pipe runs and the two coldest running units are about 6 metres from the outdoor unit with very direct pipe runs and the others are a further 15 metres with a more convoluted pipe run so you are 100% correct.
I will end my experiments with aircon at this point!
Thanks again for your help.
-
26-06-2022, 11:05 PM #6
Re: Mitsubishi FDC250VS & four FDT60
No problem, glad it helped!
There is a bit of liberty with the positioning of the branch pipes but it certainly seems yours are a step too far unfortunately. I guess the main run should have gone midway then branched off and double back to the nearest units (the units already cold) as well as onwards to the two furthest units. It could be repiped in principle, perhaps worth considering if you have the funds but best get the runs checked first against manufacturers install recommendations.
If you need a recommendation let me know where you're based and depending where you are could point you in the right direction.
Otherwise make sure the filters are clear on the units and only other thing I can think of to cause the issue is of you have lost some refrigerant but need to weigh it out to confirm ideally, otherwise run full pelt and check discharge temp of outdoor unit on controller, should be below 100°C. Give you something to fiddle with anyhow. :-)
Cheers,
Andy.