[Mott Rettop]

Hi,

I have a new mini-split installed for the upstairs and when in heat mode it controls both heads at +6 above the setpoints.

In AC mode it controls temperature just fine. This problem only exists in heat mode :-(

The heat pump is a 3MXS24RMVJUA and one of the heads in 9K BTU and the other is 12K BTU

Daikin tried to blame it on the WiFi but that can be disconnected and the problem remains...

Here's a link to a guy with the same problem last year: (cant post links? - Search "Daiken Temperature Offset")

/hvac-talk.---/vbb/threads/2244114-Daikin-temperature-offset

This system(s) is sitting there reporting the correct room temperature and yet it controls at 6 degrees off the setpoint!

You couldn't design a system with a stupider failure mode!!!! Nice going Daikin!!

Thanks!

 

[Mott Rettop]

No...according to the installers.

If there was it would only be for Heat mode (which seems odd!)

Thanks!

 

[Mott Rettop]

Hi,

is that why I only got 1 reply on a subject I would have thought would get dozens?

 

[Mott Rettop]

Yea...I would think that is pretty stupid, if air is moving in the room, that plan falls apart!

Anyway Daikin said it should be mounted at 6' and since this is a cape cod then it had to be about 4'. I can't see that making a difference of 6 degrees on the plus side though!

 

[Mott Rettop]

Problem is I need it to work in Auto mode as it's in the Mother-in-law's area. I would never be able to explain all of the things she would need to do, whether in AC or Heat mode, if I just ran it with an offset.

 

[Mott Rettop]

Both rooms it's servicing are facing the sun, they should both experience the same external perturbations.
(both setpoints are only degrees apart and stay set that way)

I'm an EE and for the life of me can't see why that would be a very hard to control situation ��

 

[Mott Rettop]

Yea...they said they did. Now they put me on a waiting list for a Daikin "roving expert" to come out and look at it. (the installers have come out 4 times I should add, each time I explained the problem completely and no one seems to get it, as in the possible suggestions about why are really very poor)

I'm losing faith in humanity at this point...

 

[Mott Rettop]

I need auto mode to work!

 

[Mott Rettop]

If the air is moving in the room that shouldn't matter (the height)...

 

[Mott Rettop]

It's a Cape Cod so that's not an option and since there is air moving in the rooms (ceiling fans) how would that even matter much if at all?

 

[Mott Rettop]

I'm hoping there are other folks who have experienced the same issue (besides the one I already pointed out)...

Accepting it like it is is not an option since I need auto mode to work!

 

[Mott Rettop]

If 4' is low for the head, does that imply if I simply move it 2 feet up it'll correct a 6 degree offset problem?

What about AC mode...under those same conditions, I would expect it to have a problem too, but it is perfect!

 

[Mott Rettop]

I could see that cause a 2-3 degree offset, MAX, but not six degrees!

It would also have some effect on AC mode...but that works perfect!

 

[Mott Rettop]

Yes...

It problem is only in heat mode, in AC mode it cools both rooms very closely to the setpoint with no issues (well within less than 2 degrees!)

This is what I don't understand!! (If it was simply an offset problem in both modes, that would be easy to understand!!)

 

[Mott Rettop]

Yes both are in heat mode...otherwise it does nothing! (which is totally understandable!)

It also does the same thing if I only run either one of them by themselves....

 

[Mott Rettop]

I'm not sure how they sized it but I can tell you that it is somewhat oversized but in cooling mode it needs to remove the heat from the entire roof while in heat mode if has an easy time being on the second floor (Cape Cod).

So while it's a bit oversized in heat mode in cooling mode it's a blessing...

The thing about this problem is it maintains exactly a 6 degree offset no matter how cold it is outside. If there were a sizing issue the magnitude of the problem would likely change as well!

This seems like a control issue straight up. To me all the worry about the thing needing to be 2' higher is the same as saying that there is that much of a temperature gradient in the room.

That also falls apart when there is air moving in the room (such as a ceiling fan running).

The other thing about the sizing issue is it runs just the same with a window open...if it was a sizing issue the problem should go away right there!

 

[Mott Rettop]

If I open a window that is the same as a larger room...it still behaves the same under those conditions.

That cannot be the only cause. The problem would also not remain fixed at 6 degrees off over the range of outdoor temperatures it has seen so far.

If I'm wrong thinking this I would love to get straightened out!

Thanks!

 

[Mott Rettop]

Sure if you tell me what parts to focus on!

 

[Mott Rettop]

There is 4 feet under them, and just above them the walls turn to ceiling, sloped up like any cape cod.

If you're claiming it's too low then you are not hearing that when the air is moving that argument goes out the window same as it being oversized.

I can run it with a window open (simulates a larger room) and it will still heat the room exactly 6 degrees too high!!

Anyway, It doesn't seem I'm able to post a pic...but you get the idea!

Thanks!

 

[Mott Rettop]

If there is an offset due to height why is there no problem at all in AC mode?

Also if that was the problem wouldn't turning on a fan in the room change the resulting temperature since the air is no longer stratified?