Mini Split performance issue

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Old 01-19-16, 08:39 AM
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Mini Split performance issue

I have two mini splits from the same company, one 12k and one 18k. Since the day they were bought the 18k does not perform correctly. I have a friend who bought an 18k at the same time and is having the same issues. Basically the 18k does not heat nearly as well as the 12k.

The symptoms and checks to date for the 18k are as follows.

- The lower the outside temp goes, the slower the variable speed compressor runs. (shouldn't this be opposite?)
- At the same outside temps, the 12k puts out easily double the heat of the 18K.
- All sensors have been checked and are working within spec.
- Unit has been recovered and recharged 3 times (once with completely new 410a) with no sign of leaks.
- compressor rating in the 12k is 11k. Compressor rating in the 18k is 13k. (How can this be right?)
- Both indoor and outdoor control boards have been replaced (however the boards did not come in original packaging so maybe the replacements are faulty?)
- Indoor fan speed does not appear to run correctly in heat mode. I have nothing to base this on other than how the 12k works.
- compressor is rated to draw 10.5A at full load, yet it has never drawn more than 7A, even in warmer weather. The 12k is rated to draw 6.5A and it will draw that until the indoor unit is up to temp.

To be clear, I am not looking for charging instructions, or even diagnosing instructions, I can figure that stuff out myself. However, I do need to be pointed in the right direction as to what I should look for and check. Does anyone have any ideas as to what the problem might be?
 
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Old 01-19-16, 04:59 PM
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Is the 12k variable speed too? (Just trying to get some kind of comparison standard happening here)
 
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Old 01-19-16, 06:37 PM
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Yes, the 12K is also variable speed. Both units are virtually identical except for their BTU rating. They both have the exact same look (except size obviously) and features.
 
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Old 01-19-16, 07:54 PM
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Are these straight heatpumps.... no reheat elements ?
 
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Old 01-20-16, 03:25 AM
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Yes, stright up heat pump with no backup elements.
 
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Old 01-21-16, 10:30 PM
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I am not the expert about mini splits that others are here but I have been watching home improvement shows. On either This Old House or Ask This Old House their plumber Richard Trethewey said that the outdoor unit couldn't be but so many feet away from the indoor unit. I don't unfortunately remember exactly how many feet is maximum distance but it is worth searching online to find out. It could be you need yet another unit to solve your problem.
 
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Old 01-22-16, 06:10 AM
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In both cases the outdoor unit is less than 10 feet from the indoor unit. To be clear, these are two completely separate units with their own in door and outdoor unit.
 
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Old 01-22-16, 07:07 AM
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Have you contacted the installer, retailer, distributor, manufacturer ?
 
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Old 01-22-16, 08:24 AM
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I have had two techs look at it and did not see where the problem was. Been in contact with the manufacturer and they dont have any answers. They just say to have a tech look at it. Maybe if they were given enough time, a tech could pinpoint the problem, but it would cost more to pay someone to strip the unit down and diagnose every part than what the unit is worth. Besides, I am beginning to think it is a problem with the unit design rather than a malfunction since two were bought at the same time and both operate the same way.
 
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Old 01-23-16, 07:43 AM
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Who is the manufacturer ? What are the model numbers ?
 
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Old 01-23-16, 11:49 AM
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The Manufacture is Senville. To my knowledge they are made by Daikin and re branded, but not positive. I have the 18k and 12k Aura Series shown at Senville.com

I am well aware that these are not top shelf units, however, I do expect a larger unit to perform better than a smaller one of the same brand. As I stated, the 12k works perfectly to heat the upstairs of my home, around 700sqft. The downstairs is all one open space of around 1,000sqft.
 
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Old 01-25-16, 05:00 AM
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Different models perform better at different temps. To my knowledge Mitsubishi has the best BTU output -5 degrees. But then you have to get the correct model to do that. What did the HVAC company say your system could go down to and how many BTUs?
 
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Old 01-25-16, 05:09 AM
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Copied from the install manual. Never seen this on a Daikin unit.

Suggestion:
For the unit adopts an Electric Heater, when the outside ambient temperature
is below 0 C(32 F), we strongly recommend you to keep themachinepluggedin order to
guarantee it running smoothly
 
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Old 01-25-16, 06:39 AM
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Here is the AHRI rating for each unit.

12K https://senville.com/certificates/SENA-12HF-AHRI.pdf
18K https://senville.com/certificates/SENA-18HF-AHRI.pdf

The reason I say the 18k indoor fan does not run correctly is because it seems the higher I run the fan speed, the slower the compressor runs, and therefore the less heat that is put out. This is opposite from what the 12K unit does (higher fan speed, higher compressor speed).
 
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Old 01-25-16, 08:49 AM
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Thats a huge drop off in heating performance the lower the temp. Thats less than half capacity at 17. what does 5 look like? does it even heat that low?
 
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Old 01-25-16, 10:49 AM
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I dont have the technical info for 5, but based on my experience the 12K does still heat well. The 18K nothing much at all at those temps.

Again, I understand these are not top shelf units, which was reflected in the purchase price. I am just wondering what could be causing one to heat so radically different than the other.
 
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Old 01-26-16, 08:59 AM
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idle thoughts...

- perhaps there's a manufacturer control software bug (as you've surmised earlier): "oops, speed up instead of down" would be an easy mistake to make in the software world where there's often hardware / software misunderstandings.
Are the control boards in the 12k and 18k units the same ? Maybe some clues can be gleaned by inspection / swapping .
Is there a distributor who's tech rep would be willing to talk to you and see if there's a firmware update ?

- wiring error so that compressor speed control somehow gets "inverted" signal from blower speed control
Have you been able to find schematics / wiring diagrams for these units ?

The AHRI ratings should give one confidence, but AHRI may not do any testing and just lists what the manufacturer tells them.

Have you considered a complaint to local consumer protection agency if indeed there's no help from the manufacturer / vendor chain ?
 
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Old 01-26-16, 11:23 AM
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Thanks for the input.

I originally thought that it was definitely a software error, but even after swapping both boards, there is no difference in operation. The revision date on the two boards I have is also two years apart (they sent me an older board as a replacement.) The board in the 12K is a different size and configuration, although all the connectors look to be the same type. The strange thing is the system seems to operate completely normal in cooling mode.

There are no techs/installers for the company in my area, though I have considered contacting some in other areas to see if they could give me their opinions.

I do have the schematics and wiring diagrams for my units.

I have not gone to the BBB yet, I am still waiting to hear back from the manufacturer. I would rather they work with me on this first.
 
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Old 01-27-16, 08:18 AM
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can you tell from the schematics what happens when the fan speed is increased - how is that information sent to the compressor unit ? One can imagine a DC signal with the wires reversed (long shot I know).

Perhaps the TXV used in the heatpump mode (assuming there is one) is not functioning correctly (e.g. improperly mounted, bad insulation, debris in system ... during the rechargings did the superheat get measured ? - supposedly this is way to tell if the refrigerant flows / TXV are ok ... certified tech available ?

What about defrost cycles ? Do they occur at reasonable times - so that the outdoor exchanger is mostly free of ice .... do you know if this is demand defrost or timed ? If demand, then maybe the controlling sensors or their connections or locations are faulty ... Perhaps the strangeness in fan speeds that you observe is the actions during a defrost cycle - and if you are getting too many of them the heating surely suffers.
 
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Old 01-27-16, 08:32 AM
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The schematics I have are not that detailed, they are only a general schematic of each board and and what is on it, not how the circuits interact with each other.

I thought there may be an issue with the TXV insulation, and opened up the unit to check, but it seems to be well covered. Superheat was not checked when the unit was recharged. It was simply weighed in. It was a certified tech who did the recharging.

Defrost cycles are by demand, and seem to come on a reasonable times. The outdoor unit is kept free of frost or ice except for a very small band at the very bottom of the coil that tends to stay icy. I have pulled and checked all the sensors in the unit and all are reading proper resistance based on the specs in the service manual.

A few more things to note about how the unit runs. When in heat mode, the unit will not shut off when it has reached the set point temp, it will just keep on heating. The 12K will shut the compressor off and go to minimum indoor fan speed when set point is reached. When set to auto fan speed, the fan will not go beyond low speed. If set to "turbo" mode (which is supposed to make the unit run at max capacity until the setpoint is reached) the fan speed will run at maximum, even though the compressor only runs at about 3/4 speed, and does not slow down when the set point is reached.

Is it possible I was set a faulty board as a replacement? Would it most likely be the indoor or outdoor board that would cause these issues?
 
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Old 01-28-16, 07:33 AM
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Presumably the thermostat which controls the compressor on/off is located in the inside unit - and it sounds like either the inside controls are faulty or its signals are somehow ignored / garbled at the outside unit.
The fact that the inside fan speeds up when you expect slowdown makes one suspicious of the inside control board ; is the inside control board the same as the one on the 12k by any chance ?
No doubt you've checked and double checked the control wiring and the connections ...

It's sure not unknown for replacement boards to be faulty, and it's a bit discouraging that the replacement you received was an earlier version than the one you already had.
 
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